#include<bits/stdc++.h>
using namespace std;
int dp[1405][1405];
int main(){
    int h, w; cin >> h >> w;
    for (int i = 0; i < h; i++)
    {
        for (int j = 0; j < w; j++)
        {
            bool c; cin >> c;
            dp[i][j] = !c;
        }
    }
    for (int i = 1; i < h; i++)
    {
        for (int j = 0; j < w; j++)
        {
            dp[i][j] = dp[i-1][j] * dp[i][j] + dp[i][j];
        }
    }
    
    stack<pair<int, int>> S;
    int ans = 0;
    for (int i = 0; i < h; i++)
    {
        for (int j = 0; j <= w; j++)
        {  
            if (S.empty()){S.push(make_pair(dp[i][j], j));continue;}

            if (S.top().first < dp[i][j])
            {
                S.push(make_pair(dp[i][j], j));
            }else if(S.top().first > dp[i][j])
            {
                int target = j;
                while ((!S.empty()) && S.top().first >= dp[i][j])
                {
                    pair<int,int> num = S.top();S.pop();
                    ans = max(ans, (j-num.second) * num.first);
                    target = num.second;
                }
                S.push(make_pair(dp[i][j], target));
            }
        }
        
    }
    cout << ans << endl;
    
}
