#include <bits/stdc++.h>
using ll = long long;
int const nmax = 2500;
std::string s[5 + nmax];
int dp[5 + nmax], dp_left[5 + nmax][5 + nmax], dp_right[5 + nmax][5 + nmax], dp_up[5 + nmax][5 + nmax], dp_down[5 + nmax][5 + nmax];
int main() {
std::ios_base::sync_with_stdio(0);
std::cin.tie(0);
int n, m;
std::cin >> n >> m;
for(int i = 1;i <= n; i++) {
std::cin >> s[i];
s[i] = "#" + s[i];
}
for(int i = 1;i <= n; i++)
for(int j = 1;j <= m; j++) {
if(s[i][j] == '1') {
dp_left[i][j] = dp_left[i][j - 1] + 1;
dp_up[i][j] = dp_up[i - 1][j] + 1;
}
}
for(int i = n; 1 <= i; i--)
for(int j = m; 1 <= j; j--) {
if(s[i][j] == '1') {
dp_right[i][j] = dp_right[i][j + 1] + 1;
dp_down[i][j] = dp_down[i + 1][j] + 1;
}
}
for(int i = 1;i <= n; i++)
dp[i] = m + 1;
int h = n;
for(int i = 1;i <= n; i++)
for(int j = 1;j <= m; j++)
if(s[i][j] == '1') {
h = std::min(h, dp_up[i][j] + dp_down[i][j] - 1);
dp[1] = std::min(dp[1], dp_left[i][j] + dp_right[i][j] - 1);
}
for(int j = 1;j <= m; j++) {
int cnt = 0, left = 0, right = m + 1;
for(int i = 1;i <= n; i++) {
if(s[i][j] == '1') {
left = std::max(left, j - dp_left[i][j] + 1);
right = std::min(right, j + dp_right[i][j] - 1);
cnt++;
dp[cnt] = std::min(dp[cnt], right - left + 1);
} else {
cnt = 0;
left = 0;
right = m + 1;
}
}
}
for(int j = 1; j <= m; j++) {
int cnt = 0, left = 0, right = m + 1;
for(int i = n; 1 <= i; i--) {
if(s[i][j] == '1') {
left = std::max(left, j - dp_left[i][j] + 1);
right = std::min(right, j + dp_right[i][j] - 1);
cnt++;
dp[cnt] = std::min(dp[cnt], right - left + 1);
} else {
cnt = 0;
left = 0;
right = m + 1;
}
}
}
int result = 0;
for(int i = 1;i <= h; i++) {
if(i > 1)
dp[i] = std::min(dp[i], dp[i - 1]);
result = std::max(result, dp[i] * i);
}
std::cout << result << "\n";
return 0;
}
