#include <bits/stdc++.h>
#define v(i,a,b) for(int i=a;i<b;i++)
using namespace std;
int dp[500][500],top[500],h,w;
int main(){char z;while(true){cin>>h>>w;if(h==0&&w==0)break;v(i,0,h)top[i]=0;v(j,0,w){cin>>z;dp[0][j]=1;if(z=='*')dp[0][j]=0;top[j]=max(top[j],dp[0][j]);}v(i,1,h)v(j,0,w){cin>>z;dp[i][j]=dp[i-1][j]+1;if(z=='*')dp[i][j]=0;top[i]=max(top[i],dp[i][j]);}bool t[500];int ans=0;v(i,0,h){v(j,0,w)t[j]=1;v(j,1,top[i]){v(k,0,w)if(dp[i][k]==j-1)t[k]=0;int best=0,cnt=0;v(k,0,w){if(t[k])cnt++;else{best=max(best,cnt);cnt=0;}}best=max(best,cnt);ans=max(ans,best*j);}}cout<<ans<<endl;}return 0;}