3 4
1011
1001
0001
3 4
1010
1001
0001

4
2

Note: Huge Input, scanf() is recommended.

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int const MAX = 1e3 + 5;
int const INF = 0x3fffffff;
char s[MAX][MAX];
int cnt[MAX][MAX];
int dp[MAX];
int n, m;

bool cmp(int a, int b)
{
    return a > b;
}

int main()
{
    while(scanf("%d %d", &n ,&m) != EOF)
    {
        memset(cnt, 0, sizeof(cnt));
        memset(dp, 0, sizeof(dp));
        for(int i = 1; i <= n; i++)
            scanf("%s", s[i] + 1);
        for(int i = n; i >= 1; i--)
            for(int j = 1; j <= m; j++)
                if(s[i][j] - '0')
                    cnt[i][j] = cnt[i + 1][j] + 1;
        for(int i = 1; i <= n; i++)
        {
            sort(cnt[i] + 1, cnt[i] + 1 + m, cmp);
            for(int j = 1; j <= m; j++)
                if(cnt[i][j])
                    dp[i] = max(dp[i], j * cnt[i][j]);
        }
        int ans = 0;
        for(int i = 1; i <= n; i++)
            ans = max(ans, dp[i]);
        printf("%d\n", ans);
    }
}