//#define LOCAL

 #include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 using namespace std;

 const int maxn = ;

 char map[maxn][maxn];

 int h[maxn], temp[maxn];

 int main(void)

 {

     #ifdef LOCAL

         freopen("2830in.txt", "r", stdin);

     #endif

     int row, col;

     while(scanf("%d%d", &row, &col) == )

     {

         int i, j;

         for(i = ; i < row; ++i)

             scanf("%s", map[i]);

         memset(h, , sizeof(h));

         int ans = ;

         for(i = ; i < row; ++i)

         {

             for(j = ; j < col; ++j)

             {

                 if(map[i][j] == '')

                     ++h[j];

                 else

                     h[j] = ;

             }

             memcpy(temp, h, sizeof(h));

             sort(temp, temp + col);

             for(j = ; j < col; ++j)

                 ans = max(ans, (col-j)*temp[j]);

         }

         printf("%d\n", ans);

     }

     return ;

 }