#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
assert(n == 1);
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;
}
}
vector<int> mx(m + 1, n);
for (int i = 0; i < n; i++) {
vector<int> stk;
for (int j = 0; j < m; j++) {
if (s[i][j] == '0') {
while (!stk.empty()) {
int l = j - stk.back();
mx[l] = min(mx[l], len[i][stk.back()]);
stk.pop_back();
}
continue;
}
while (!stk.empty() && len[i][stk.back()] >= len[i][j]) {
int l = j - stk.back() + 1;
mx[l] = min(mx[l], len[i][j]);
stk.pop_back();
}
if (!stk.empty()) {
int l = j - stk.back() + 1;
mx[l] = min(mx[l], len[i][stk.back()]);
}
stk.push_back(j);
}
while (!stk.empty()) {
int l = m - stk.back();
mx[l] = min(mx[l], len[i][stk.back()]);
stk.pop_back();
}
}
for (int i = 0; i < n; i++) {
vector<int> stk;
for (int j = m - 1; j >= 0; j--) {
if (s[i][j] == '0') {
while (!stk.empty()) {
int l = stk.back() - j;
mx[l] = min(mx[l], len[i][stk.back()]);
stk.pop_back();
}
continue;
}
while (!stk.empty() && len[i][stk.back()] >= len[i][j]) {
int l = stk.back() - j + 1;
mx[l] = min(mx[l], len[i][j]);
stk.pop_back();
}
if (!stk.empty()) {
int l = stk.back() - j + 1;
mx[l] = min(mx[l], len[i][stk.back()]);
}
stk.push_back(j);
}
while (!stk.empty()) {
int l = stk.back() + 1;
mx[l] = min(mx[l], len[i][stk.back()]);
stk.pop_back();
}
}
for (int i = 1; i < m; i++) {
mx[i + 1] = min(mx[i + 1], mx[i]);
}
int res = n * m;
for (int i = 1; i <= m; i++) {
res = min(res, mx[i] * i);
}
cout << res << '\n';
return 0;
}
