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>
using namespace std;
bool isprime(long long int n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
vector<long long int> prime;
void sieve(long long int n) {
  bool bakh[n + 1];
  memset(bakh, true, sizeof(bakh));
  for (long long int p = 2; p * p <= n; p++) {
    if (bakh[p] == true) {
      for (long long int i = p * p; i <= n; i += p) bakh[i] = false;
    }
  }
  for (long long int p = 2; p <= n; p++)
    if (bakh[p]) prime.push_back(p);
}
long long int eulertotient(long long int z) {
  long long int fac = z;
  for (long long int i = 0; prime[i] * prime[i] <= z; i++) {
    if (z % prime[i] == 0) {
      fac -= (fac / prime[i]);
      while (z % prime[i] == 0) z /= prime[i];
    }
  }
  if (z > 1) fac -= (fac / z);
  return fac;
}
long long int power(long long int x, long long int y, long long int p) {
  long long int res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long int gcd(long long int a, long long int b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
long long int lcm(long long int a, long long int b) {
  long long int g = gcd(a, b);
  long long int ans = (a * b) / g;
  return ans;
}
long long int modInverse(long long int a, long long int m) {
  long long int hvf = gcd(a, m);
  if (hvf == 1) return power(a, m - 2, m);
  return -1;
}
void multiply(long long int F[2][2], long long int M[2][2]) {
  long long int x = F[0][0] * M[0][0] + F[0][1] * M[1][0];
  long long int y = F[0][0] * M[0][1] + F[0][1] * M[1][1];
  long long int z = F[1][0] * M[0][0] + F[1][1] * M[1][0];
  long long int w = F[1][0] * M[0][1] + F[1][1] * M[1][1];
  F[0][0] = x;
  F[0][1] = y;
  F[1][0] = z;
  F[1][1] = w;
}
void powermat(long long int F[2][2], long long int n) {
  if (n == 0 || n == 1) return;
  long long int M[2][2] = {{1, 1}, {1, 0}};
  powermat(F, n / 2);
  multiply(F, F);
  if (n % 2 != 0) multiply(F, M);
}
long long int fib(long long int n) {
  long long int F[2][2] = {{1, 1}, {1, 0}};
  if (n == 0) return 0;
  powermat(F, n - 1);
  return F[0][0];
}
vector<long long int> merge(vector<long long int> v1,
                            vector<long long int> v2) {
  vector<long long int> temp;
  long long int i = 0, j = 0;
  while (i < v1.size() && j < v2.size()) {
    if (v1[i] < v2[j])
      temp.push_back(v1[i]), i++;
    else
      temp.push_back(v2[j]), j++;
  }
  while (i < v1.size()) temp.push_back(v1[i]), i++;
  while (j < v2.size()) temp.push_back(v2[j]), j++;
  return temp;
}
string ar[5005];
long long int dp[5005][5005], n, m;
long long int fun(long long int id) {
  stack<long long int> st;
  long long int i = 0, ans = 0;
  while (i < m) {
    if (st.size() == 0 || dp[id][st.top()] <= dp[id][i])
      st.push(i);
    else {
      while (!st.empty() && dp[id][st.top()] > dp[id][i])
        ans = max(ans, dp[id][st.top()] * (i - st.top())), st.pop();
    }
    i++;
  }
  while (!st.empty()) {
    ans = max(ans, dp[id][st.top()] * (m - st.top())), st.pop();
  }
  return ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  cin >> n >> m;
  for (long long int i = 0; i < n; i++) cin >> ar[i];
  for (long long int j = m - 1; j >= 0; j--) {
    for (long long int i = 0; i < n; i++) {
      if (j == m - 1)
        dp[i][j] = (ar[i][j] == '1');
      else
        dp[i][j] = (ar[i][j] == '1') ? (1 + dp[i][j + 1]) : 0LL;
    }
  }
  long long int ans = 0;
  for (long long int j = m - 1; j >= 0; j--) {
    vector<long long int> vect;
    for (long long int i = 0; i < n; i++) {
      vect.push_back(dp[i][j]);
    }
    sort(vect.begin(), vect.end());
    for (long long int i = 0; i < n; i++) {
      ans = max(ans, vect[i] * (n - i));
    }
  }
  cout << ans << endl;
}
