#include "bits/stdc++.h"
using namespace std;
#define ff first
#define ss second
#define all(v) v.begin(), v.end()
#define ll long long
#define pb push_back
#define pii pair<int, int>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define tr(i, c) for(auto i = c.begin(); i != c.end(); ++i)
#define wr puts("----------------")
template<class T>bool umin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool umax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
const int N = 2505;
int cep[N][N], sag[N][N], up[N][N], as[N][N], c[N];
char a[N][N];
int main(){
int n, m;
scanf("%d%d", &n, &m);
for(int i = 1; i <= n; ++i)
for(int j = 1; j <= m; ++j)
scanf(" %c", &a[i][j]);
for(int i = 1; i <= n; ++i){
for(int j = 1; j <= m; ++j)
cep[i][j] = (a[i][j]=='1'?cep[i][j-1]+1:0);
for(int j = m; j >= 1; --j)
sag[i][j] = (a[i][j]=='1'?sag[i][j+1]+1:0);
}
for(int j = 1; j <= m; ++j){
for(int i = 1; i <= n; ++i)
up[i][j] = (a[i][j]=='1'?up[i-1][j]+1:0);
for(int i = n; i >= 1; --i)
as[i][j] = (a[i][j]=='1'?as[i+1][j]+1:0);
}
int A = n, B = m;
for(int i = 1; i <= n; ++i)
for(int j = 1; j <= m; ++j)
if(a[i][j] == '1')
umin(A, up[i][j]+as[i][j]-1), umin(B, cep[i][j]+sag[i][j]-1);
for(int i = 1; i <= A; ++i)
c[i] = B;
for(int i = 1; i <= n; ++i)
for(int j = 1; j <= m; ++j){
if(a[i][j] != '1')
continue;
int now = B;
if(as[i][j]==1)
for(int k = i; k >= i-A+1; --k){
if(cep[i][j]==1)
umin(now, sag[k][j]), umin(c[i-k+1], now);
if(sag[i][j]==1)
umin(now, cep[k][j]), umin(c[i-k+1], now);
}
else if(up[i][j]==1)
for(int k = i; k <= i+A-1; ++k){
if(cep[i][j]==1)
umin(now, sag[k][j]), umin(c[k-i+1], now);
if(sag[i][j]==1)
umin(now, cep[k][j]), umin(c[k-i+1], now);
}
}
int answer = 0;
for(int i = 1; i <= A; ++i)
umax(answer, i*c[i]);
printf("%d\n", answer);
}
