#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ff first
#define ss second
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define INF 0x3f3f3f3f
#define MOD 1000000007
#define N 2505
int a[N][N];
int up[N][N], le[N][N];
vector<pair<int, int> > v;
int ans[N][N], h[N];
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m;
cin>>n>>m;
for(int i = 1; i <= n; ++i){
for(int j = 1; j <= m; ++j){
char c;
cin>>c;
a[i][j] = c - '0';
}
}
int mx= 2500;
for(int i = 1; i <= m; ++i){
for(int j = 1; j <= n; ++j){
if(a[j][i] == 0) up[j][i] = 0;
else up[j][i] = up[j - 1][i] + 1;
if(a[j + 1][i] == 0 && a[j][i] == 1)mx = min(mx, up[j][i]);
}
}
memset(ans, 0x3f, sizeof ans);
memset(h, 0x3f, sizeof h);
v.push_back({0, 0});
for(int i = 1; i <= n; ++i){
for(int j = 1; j <= m + 1; ++j){
int t = 0;
while(v.back().ff > up[i][j]){
t += v.back().ss;
v.pop_back();
ans[max(up[i][j], v.back().ff) + 1][i] = min(ans[max(up[i][j], v.back().ff) + 1][i], t);
}
if(v.back().ff == up[i][j]){
v.back().ss += 1 + t;
} else {
v.push_back({up[i][j], 1 + t});
}
}
}
int res = 0;
for(int i = 1; i <= mx; ++i){
for(int j = i; j <= n; j++){
h[i] = min(h[i], ans[i][j]);
ans[i + 1][j] = min(ans[i + 1][j], ans[i][j]);
}
res = max(res, h[i] * i);
}
cout<<res;
}
