#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
vector<string> s(n);
for (int i = 0; i < n; i++) {
cin >> s[i];
}
vector<vector<int>> U(n, vector<int>(m));
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
continue;
}
U[i][j] = (i == 0 || s[i - 1][j] == '0' ? i : U[i - 1][j]);
}
}
vector<vector<int>> D(n, vector<int>(m));
for (int i = n - 1; i >= 0; i--) {
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
continue;
}
D[i][j] = (i == n - 1 || s[i + 1][j] == '0' ? i : D[i + 1][j]);
}
}
vector<vector<int>> len(n, vector<int>(m));
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
continue;
}
len[i][j] = D[i][j] - U[i][j] + 1;
}
}
int width = m;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
continue;
}
int ptr = j;
while (ptr + 1 < m && s[i][ptr + 1] == '1') {
ptr += 1;
}
width = min(width, ptr - j + 1);
j = ptr;
}
}
int height = n;
for (int j = 0; j < m; j++) {
for (int i = 0; i < n; i++) {
if (s[i][j] == '0') {
continue;
}
int ptr = i;
while (ptr + 1 < n && s[ptr + 1][j] == '1') {
ptr += 1;
}
height = min(height, ptr - i + 1);
i = ptr;
}
}
vector<int> mx(m + 1, height);
for (int i = 0; i < n; i++) {
int bef = -1;
int val = (int) 1e9;
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
bef = j;
val = (int) 1e9;
continue;
}
val = min(val, len[i][j]);
mx[j - bef] = min(mx[j - bef], val);
}
}
for (int i = 0; i < n; i++) {
int bef = m;
int val = (int) 1e9;
for (int j = m - 1; j >= 0; j--) {
if (s[i][j] == '0') {
bef = j;
val = (int) 1e9;
continue;
}
val = min(val, len[i][j]);
mx[bef - j] = min(mx[bef - j], val);
}
}
for (int i = 1; i < width; i++) {
mx[i + 1] = min(mx[i + 1], mx[i]);
}
int res = 0;
for (int i = 1; i <= width; i++) {
res = max(res, mx[i] * i);
}
cout << res << '\n';
return 0;
}
