#include<cstdio>

 #include<cmath>

 #include<algorithm>

 #include<cstring>

 #include<iostream>

 int n,m,a[][],h[][];

 char s[];

 int read(){

     int t=,f=;char ch=getchar();

     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}

     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}

     return t*f;

 }

 int main(){

     n=read();m=read();

     for (int i=;i<=n;i++){

         scanf("%s",s+);

         for (int j=;j<=m;j++)

          a[i][j]=s[j]-'';

     }

     for (int i=;i<=n;i++)

      for (int j=;j<=m;j++){

         if (a[i][j]) continue;

         if (i!=&&a[i-][j]==) h[i][j]=h[i-][j]+;

         else h[i][j]=;

      }

     int ans=;

     for (int i=;i<=n;i++)

      for (int j=;j<=m;j++)

       if (a[i][j]==)

      {

         int ll=<<;

         for (int k=j;k>=&&a[i][k]==;k--){

             ll=std::min(ll,h[i][k]);

             ans=std::max(ans,ll+j-k+);

         }

      }

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

     return ;

 }