/*
DEATH-MATCH
Davit-Marg
*/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <cassert>
#include <vector>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <iterator>
#include <ctype.h>
#include <stdlib.h>
#include <fstream>
#define mod 1000000007ll
#define LL long long
#define LD long double
#define MP make_pair
#define PB push_back
using namespace std;
int n, m,w,h,l,r,mid;
int mp[2503][2503],pr[2503][2503];
char tmp;
int sum(int ys,int xs,int y,int x)
{
xs--;
ys--;
return pr[y][x] - pr[y][xs] - pr[ys][x] + pr[ys][xs];
}
bool check(int x)
{
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
if (mp[i][j] && !mp[i - 1][j] && !mp[i][j - 1])
{
int s = sum(i, j, i + x - 1, j + w - 1);
if (i + x - 1 > n || j + w - 1 > m)
return 0;
if (s != x * w)
return 0;
}
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
if (mp[i][j] && !mp[i + 1][j] && !mp[i][j + 1])
{
int s = sum(i-x+1,j-w+1,i, j);
if (i - x + 1 < 1 || j - w + 1 < 1)
return 0;
if (s != x * w)
return 0;
}
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
if (mp[i][j] && !mp[i - 1][j] && !mp[i][j + 1])
{
int s = sum(i, j - w + 1, i + x - 1, j);
if (i + x - 1 > n || j - w + 1 < 1)
return 0;
if (s != x * w)
return 0;
}
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
if (mp[i][j] && !mp[i + 1][j] && !mp[i][j - 1])
{
int s = sum(i - x + 1, j, i, j + w - 1);
if (j + w - 1 > m || i - x + 1 < 1)
return 0;
if (s != x * w)
return 0;
}
return 1;
}
int main()
{
cin >> n >> m;
w = m;
h = n;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
{
cin >> tmp;
mp[i][j] = tmp - '0';
pr[i][j] = pr[i - 1][j] + pr[i][j - 1] - pr[i - 1][j - 1]+mp[i][j];
}
for (int i = 1; i <= n; i++)
{
int sum = 0;
for (int j = 1; j <= m; j++)
{
sum += mp[i][j];
if (mp[i][j] == 0)
{
if (sum)
w = min(sum,w);
sum = 0;
}
}
if(sum)
w = min(sum, w);
}
r = n;
for (int i = 1; i <= m; i++)
{
int sum = 0;
for (int j = 1; j <= n; j++)
{
sum += mp[j][i];
if (mp[j][i] == 0)
{
if (sum)
r = min(sum, r);
sum = 0;
}
}
}
l = 1;
h = 1;
while (l <= r)
{
mid = (l + r) / 2;
if (check(mid))
{
h = mid;
l = mid + 1;
}
else
r = mid - 1;
}
cout << max(w * h,1) << endl;
return 0;
}
/*
5 6
000000
111110
111111
111111
000000
7 8
01001110
01001110
01001100
00000000
01000000
01000000
01000000
7 8
01000000
00000000
00000000
00000000
00000000
00000000
00000000
7 8
11111111
11111111
11111111
11100111
11111111
11111111
11111111
7 8
00000000
00011000
00011000
00000000
00011111
00011111
00000000
*/
