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
#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
const int inf = 1000000007;
const long long linf = 1LL << 62;
const unsigned long long ulinf = 1ULL << 63;
const double eps = 0.000001;
const double pi = 3.14159265358979323846;
template <class T>
T abs(T a) {
  return a >= 0 ? a : -a;
}
template <class T>
T sqr(T a) {
  return a * a;
}
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <class T>
T mod(T a, T b) {
  return (a % b + b) % b;
}
template <class T>
T lowbit(T x) {
  return x & -x;
}
long long powmod(long long a, long long b, long long c) {
  if (b == 0LL) return 1LL;
  long long ret = powmod(a, b >> 1, c);
  ret = ret * ret % c;
  if (b & 1LL) ret = ret * a % c;
  return ret;
}
long long modinv(long long a, long long b) { return powmod(a, b - 2LL, b); }
template <class T>
void maxe(T &a, T b) {
  if (a < b) a = b;
}
template <class T>
void mine(T &a, T b) {
  if (a > b) a = b;
}
int iszero(double a) { return abs(a) <= eps; }
template <class T>
void geti(T &a) {
  a = 0;
  T b = 1;
  char c = getchar();
  if (c == '-')
    b = -1;
  else
    a = c - 48;
  while ((c = getchar()) != ' ' && c != '\n') a = a * 10 + c - 48;
  a *= b;
}
void fileio_in_out() {
  freopen(".in", "r", stdin);
  freopen(".out", "w", stdout);
}
void fileio_txt() {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
}
const int N = 5050;
const int M = 222222;
const int K = 22;
int test;
int n, m, k, ans;
char str[N];
int cnt[N][N];
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> m;
  for (int i = 1; i <= n; i++) {
    cin >> str + 1;
    for (int j = 1; j <= m; j++)
      if (str[j] == '1') {
        int pos = j + 1;
        while (str[pos] == '1') pos++;
        cnt[j][pos - 1]++;
        j = pos;
      }
  }
  for (int len = m - 1; len; len--) {
    cnt[1][len] += cnt[1][len + 1];
    cnt[m - len + 1][m] += cnt[m - len][m];
    for (int i = 2, j = i + len - 1; j < m; i++, j++)
      cnt[i][j] += cnt[i][j + 1] + cnt[i - 1][j] - cnt[i - 1][j + 1];
  }
  for (int i = 1; i <= m; i++)
    for (int j = i; j <= m; j++) {
      maxe(ans, (j - i + 1) * cnt[i][j]);
    }
  cout << ans << endl;
  return 0;
}
