#include <bits/stdc++.h>
#define maxn 2510
using namespace std;
int n, m, ans, dp[maxn];
int a[maxn][maxn], up[maxn][maxn], down[maxn][maxn];
int main(){
ios_base::sync_with_stdio(0);
cout.tie(0);
cin.tie(0);
cin >> n >> m;
for(int i = 0; i < n; ++i){
dp[i+1] = 1e9;
for(int j = 0; j < m; ++j){
char tmpC;
cin >>tmpC;
a[i][j] = tmpC-'0';
}
}
for(int i = 0; i < n; ++i){
for(int j = 0; j < m; ++j){
if(a[i][j]){
up[i][j] = 1;
if(i){
up[i][j] += up[i-1][j];
}
}
}
}
int tmp=n;
for(int i = n-1; i >= 0; --i){
for(int j = 0; j < m; ++j){
if(a[i][j]){
down[i][j] = 1 + down[i+1][j];
}
}
}
for(int i = 0; i < n; ++i){
for(int j = 0; j < m; ++j){
if(!a[i][j]){
continue;
}
int frJ = j, ln = 1, maxUp = up[i][j], maxD = down[i][j];
dp[1] = min(dp[1], maxUp+maxD-1);
while(a[i][j+1]){
++j;
++ln;
maxUp = min(maxUp, up[i][j]);
maxD = min(maxD, down[i][j]);
dp[ln] = min(dp[ln], maxUp+maxD-1);
}
maxUp = 1e9, maxD = 1e9;
ln = 1;
for(int k = j; k >= frJ; --k){
maxD = min(maxD, down[i][k]);
maxUp = min(maxUp, up[i][k]);
dp[ln] = min(dp[ln], maxUp+maxD-1);
++ln;
}
tmp = min(tmp, abs(frJ-j)+1);
}
}
for(int i = 1; i <= tmp; ++i){
ans = max(ans, i*dp[i]);
}
cout << ans;
}
