#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
#define endl '\n'
#define ll long long
#define pi pair<int, int>
#define f first
#define s second
const int maxn = 2500;
int n, m;
int a[maxn][maxn], u[maxn][maxn], d[maxn][maxn];
int dp[maxn];
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
for(int i = 0; i < n; i++)
for(int j = 0; j < m; j++){
char c;
cin >> c;
a[i][j] = c - '0';
}
for(int j = 0; j < m; j++){
dp[j] = n;
u[n - 1][j] = n - 1;
for(int i = 1; i < n; i++){
d[i][j] = !a[i][j] || !a[i - 1][j] ? i : d[i - 1][j];
u[n - i - 1][j] = !a[n - i - 1][j] || !a[n - i][j] ? n - i - 1 : u[n - i][j];
}
}
for(int i = 0; i < n; i++)
for(int j = 0, l = 0, ul = n - 1, dl = 0, r = m - 1, ur = n - 1, dr = 0; j < m; j++){
if(a[i][j]){
dp[0] = min(dp[0], u[i][j] - d[i][j] + 1);
ul = min(ul, u[i][j]), dl = max(dl, d[i][j]);
dp[j - l] = min(dp[j - l], ul - dl + 1);
}else{
if(j > l) dp[j - l] = 0;
l = j + 1;
ul = n - 1, dl = 0;
}
if(a[i][m - j - 1]){
ur = min(ur, u[i][m - j - 1]), dr = max(dr, d[i][m - j - 1]);
dp[r + j + 1 - m] = min(dp[r + j + 1 - m], ur - dr + 1);
}else{
if(m - j - 1 < r) dp[r + j + 1 - m] = 0;
r = m - j - 2;
ur = n - 1, dr = 0;
}
}
int ret = 0;
for(int i = 0; i < m; i++){
if(i) dp[i] = min(dp[i], dp[i - 1]);
ret = max(ret, (i + 1) * dp[i]);
}
cout << ret << endl;
return 0;
}
