#include <bits/stdc++.h>
using namespace std;
const int N = 2505;
int n, m, a[N][N], b[N][N], c[N][N], d[N][N], f[N];
char e[N][N];
int main(){
cin >> n >> m;
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
cin >> e[i][j];
}
}
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
if(e[i][j] == '1'){
a[i][j] = a[i][j-1] + 1;
}
else {
a[i][j] = 0;
}
}
}
for(int i = 1; i <= n; i++){
for(int j = m; j >= 1; j--){
if(e[i][j] == '1'){
b[i][j] = b[i][j+1] + 1;
}
else {
b[i][j] = 0;
}
}
}
for(int j = 1; j <= m; j++){
for(int i = 1; i <= n; i++){
if(e[i][j] == '1'){
c[i][j] = c[i-1][j] + 1;
}
else {
c[i][j] = 0;
}
}
}
for(int j = 1; j <= m; j++){
for(int i = n; i >= 1; i--){
if(e[i][j] == '1'){
d[i][j] = d[i+1][j] + 1;
}
else {
d[i][j] = 0;
}
}
}
memset(f, -1, sizeof f);
int n1 = m;
for(int i = 1; i <= n; i++){
int cnt = 0, up = 0, dw = 0;
for(int j = 1; j <= m; j++){
if(e[i][j] == '1') n1 = min(n1, a[i][j] + b[i][j] - 1);
if(e[i][j] == '0'){
cnt = 0;
up = dw = N;
continue;
}
up = min(up, c[i][j]);
dw = min(dw, d[i][j]);
cnt++;
if(~f[cnt-1]) f[cnt] = min(f[cnt-1], f[cnt]);
if(~f[cnt]) f[cnt] = min(f[cnt], up+dw-1);
else f[cnt] = up+dw-1;
}
cnt = 0, up = 0, dw = 0;
for(int j = m; j >= 1; j--){
if(e[i][j] == '0'){
cnt = 0;
up = dw = N;
continue;
}
up = min(up, c[i][j]);
dw = min(dw, d[i][j]);
cnt++;
if(~f[cnt+1]) f[cnt] = min(f[cnt+1], f[cnt]);
if(~f[cnt]) f[cnt] = min(f[cnt], up+dw-1);
else f[cnt] = up+dw-1;
}
}
int ans = 0;
for(int i = 1; i <= n1; i++){
ans = max(ans, i*f[i]);
}
cout << ans;
}
