#include <bits/stdc++.h>

using namespace std;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

int sUp[205][205], sDown[205][205], n, m, arieMax, dp1[205], dp2[205];
char a[205][205], b[205][205];
int lft[205], rght[205], st[205];

void Read()
{
    fin >> n >> m;
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
    {
        fin >> a[i][j];
        b[j][i] = a[i][j];
    }
}

int Check(int s[])
{
    int maxim = 0, top = 0;
    st[++top] = 0;
    s[0] = -1;
    for(int i = 1; i <= m; i++)
    {
        while(s[i] <= s[st[top]])
            top--;
        lft[i] = i - st[top] - 1;
        st[++top] = i;
    }
    top = 0;
    st[++top] = m + 1;
    s[m + 1] = -1;
    for(int i = m; i >= 1; i--)
    {
        while(s[i] <= s[st[top]])
            top--;
        rght[i] = st[top] - i - 1;
        st[++top] = i;
    }
    for(int i = 1; i <= m; i++)
        maxim = max(maxim, s[i] *  (lft[i] + rght[i] + 1)) ;
    return maxim;
}

void Solve(char a[205][205])
{
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
            if(a[i][j] == '0')
                sUp[i][j] = sUp[i-1][j] + 1;
            else sUp[i][j] = 0;

    for(int i = n; i >= 1; i--)
        for(int j = 1; j <= m; j++)
            if(a[i][j] == '0')
                sDown[i][j] = sDown[i+1][j] + 1;
            else sDown[i][j] = 0;

    for(int i = 1; i <= n; i++)
        dp1[i] = max(dp1[i-1], Check(sUp[i]));

    for(int i = n; i >= 1; i--)
        dp2[i] = max(dp2[i+1], Check(sDown[i]));

    for(int i = 1; i < n; i++)
        arieMax = max(arieMax, dp1[i] + dp2[i + 1]);
}

int main()
{
    Read();
    Solve(a);
    swap(n, m);
    Solve(b);
    fout << arieMax << "\n";
    fout.close();
    return 0;
}