You are given a matrix consisting of digits zero and one, its size is n × m. You are allowed to rearrange its rows. What is the maximum area of the submatrix that only consists of ones and can be obtained in the given problem by the described operations?

Let's assume that the rows of matrix a are numbered from 1 to n from top to bottom and the columns are numbered from 1 to m from left to right. A matrix cell on the intersection of the i-th row and the j-th column can be represented as (i, j). Formally, a submatrix of matrix a is a group of four integers d, u, l, r (1 ≤ d ≤ u ≤ n; 1 ≤ l ≤ r ≤ m). We will assume that the submatrix contains cells (i, j) (d ≤ i ≤ u; l ≤ j ≤ r). The area of the submatrix is the number of cells it contains.

Input

The first line contains two integers n and m (1 ≤ n, m ≤ 5000). Next n lines contain m characters each — matrix a. Matrix a only contains characters: "0" and "1". Note that the elements of the matrix follow without any spaces in the lines.

Output

Print a single integer — the area of the maximum obtained submatrix. If we cannot obtain a matrix of numbers one, print 0.

Examples

Input

1 1
1


Output

1


Input

2 2
10
11


Output

2


Input

4 3
100
011
000
101


Output

2
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;

public class MaximumSubmatrix2 {

	private static final boolean DEBUG = false;

	public static void main(String[] args) {

		try {

			final InputReader in;
			final OutputWriter out;

			if (DEBUG) {

				final String fileIn = MaximumSubmatrix2.class.getSimpleName().toLowerCase() + ".in";
				final String fileOut = MaximumSubmatrix2.class.getSimpleName().toLowerCase() + ".out";

				in = new InputReader(new FileInputStream(fileIn));
				out = new OutputWriter(new FileWriter(fileOut));
			} else {

				in = new InputReader(System.in);
				out = new OutputWriter(new OutputStreamWriter(System.out));
			}

			new MaximumSubmatrix2().solve(in, out);

			out.close();

		} catch (Exception ex) {

			ex.printStackTrace();
		}
	}

	private final void solve(final InputReader in, final OutputWriter out) throws Exception {
		final int n = Integer.parseInt(in.next());
		final int m = Integer.parseInt(in.next());
		final char[][] s = new char[n][];
		for (int i = 0; i < n; ++i) {
			s[i] = in.next().toCharArray();
		}
		final int[][] nextZero = new int[n][m];
		for (int i = 0; i < n; ++i) {
			nextZero[i][m - 1] = s[i][m - 1] == '0' ? m - 1 : m;
			for (int j = m - 2; j >= 0; --j) {
				nextZero[i][j] = s[i][j] == '0' ? j : nextZero[i][j + 1];
			}
		}

		int result = 0;
		int time = 0;
		final int[] lastTime = new int[m + 1];
		final int[] count = new int[m + 1];

		for (int j = 0; j < m; ++j) {

			++time;
			int rowCount = 0;
			for (int i = 0; i < n; ++i) {
				if (nextZero[i][j] <= j) {
					continue;
				}

				++rowCount;
				if (lastTime[nextZero[i][j]] != time) {
					lastTime[nextZero[i][j]] = time;
					count[nextZero[i][j]] = 1;
				} else {
					++count[nextZero[i][j]];
				}
			}

			for (int q = j; q < m && rowCount > 0 && (m - j) * rowCount > result; ++q) {
				if (lastTime[q] == time) {
					rowCount -= count[q];
				}
				result = Math.max(result, (q - j + 1) * rowCount);
			}
		}

		out.writeln(result);
	}

	private static final class InputReader {

		private static final byte ZERO = '0';
		private static final byte NINE = '9';

		private static final int BUFFER_SIZE = 32 << 20;

		private final BufferedInputStream in;

		private byte[] buffer = new byte[BUFFER_SIZE];
		private int bufferSize = 0;
		private int offset = 0;

		private InputReader(final InputStream in) {

			this.in = (in instanceof BufferedInputStream) ? ((BufferedInputStream) in) : (new BufferedInputStream(in));
		}

		private final int read() throws Exception {
			if (offset >= bufferSize) {
				bufferSize = in.read(buffer);
				if (bufferSize <= 0) {
					return -1;
				}
				offset = 0;
			}
			return buffer[offset++];
		}

		private final boolean isWhiteSpace(final int c) {
			return c == ' ' || c == '\r' || c == 't' || c == '\n' || c == -1;
		}

		int startPos;
		int endPos;

		public String next() throws Exception {
			startPos = offset;
			int c = read();
			while (isWhiteSpace(c)) {
				startPos = offset;
				c = read();
			}
			endPos = startPos;
			while (!isWhiteSpace(c)) {
				endPos = offset;
				c = read();
			}
			return new String(buffer, startPos, endPos - startPos);
		}
	}

	private static final class OutputWriter {

		private static final String NEW_LINE = String.format("%n");

		private final Writer output;
		private final StringBuilder buffer = new StringBuilder(1 << 17);

		public OutputWriter(final Writer output) {

			this.output = output;
		}

		public void write(final int i) {

			buffer.append(i);
		}

		public void write(final String s) {

			buffer.append(s);
		}

		public void writeln(final String s) {

			buffer.append(s);
			buffer.append(NEW_LINE);
		}

		public void writeln(final long l) {

			buffer.append(l);
			buffer.append(NEW_LINE);
		}

		public void writeln(final int i) {

			buffer.append(i);
			buffer.append(NEW_LINE);
		}

		public void close() throws Exception {

			output.write(buffer.toString());
			output.flush();
			output.close();
		}
	}
}
