#include <iostream>
#include <cmath>
#include <cctype>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <deque>
#include <stack>
#include <unordered_set>
#include <sstream>
#include <cstring>
#include <iomanip>
#include <queue>
#include <unordered_map>
#include <random>
#include <cfloat>
#include <chrono>
#include <bitset>
#include <complex>
#include <immintrin.h>
#include <cassert>
bool good(std::string* str, int32_t n, int32_t m, int32_t ans_h, int32_t ans_w) {
int32_t** sums = new int32_t*[n];
for(int32_t i = 0; i < n; i++) {
sums[i] = new int32_t[m];
for(int32_t j = 0; j < m; j++)
sums[i][j] = 0;
}
for(int32_t i = 0; i <= n - ans_h; i++) {
for(int32_t j = 0; j <= m - ans_w; j++) {
int32_t sum = 0;
for(int32_t k = i; k < i + ans_h; k++)
for(int32_t q = j; q < j + ans_w; q++) {
sum += str[k][q] - '0';
}
if(sum != ans_h * ans_w)
continue;
for(int32_t k = i; k < i + ans_h; k++)
for(int32_t q = j; q < j + ans_w; q++) {
sums[k][q]++;
}
}
}
bool good = true;
for(int32_t i = 0; i < n; i++)
for(int32_t j = 0 ;j < m; j++)
if(str[i][j] == '1' && sums[i][j] == 0)
good = false;
return good;
}
//#define TEST
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(0);
int32_t n, m;
std::cin >> n >> m;
std::mt19937 rng;
for(int32_t z = 0; z < 1; z++) {
std::string* str = new std::string[n];
for(int32_t i = 0; i < n; i++)
#ifndef TEST
std::cin >> str[i];
#else
for(int32_t j = 0; j < m; j++)
str[i].push_back(rng() % 10 < 9 ? '1' : '0');
#endif
int32_t ans2 = 0;
int32_t max_w = m;
for(int32_t i = 1; i <= n; i++) {
while(max_w > 0 && !good(str, n, m, i, max_w))
max_w--;
ans2 = std::max(ans2, i * max_w);
}
std::cout << ans2;
#ifdef TEST
int32_t ans = 0;
for(int32_t i = 1; i <= n; i++)
for(int32_t j = 1; j <= m; j++)
if(good(str, n, m, i, j))
ans = std::max(ans, i * j);
std::cout << ans << "\n";
int a = 0;
if(ans != ans2)
a++;
#endif
}
return 0;
}
/*
11111
11111
11011
01111
00111
*/
