#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define maxn 505
using namespace std;
int n,m;
int sum[maxn],high[maxn][maxn];
char map[maxn][maxn];
void init()
{
	scanf("%d%d",&n,&m);
	for (int i=1;i<=n;++i)
		scanf("%s",map[i]+1);
	/*for (int i=1;i<=n;++i)
	{
		for (int j=1;j<=m;++j)
			cout<<map[i][j];
		cout<<endl;
	}*/
}
void solve()
{
	int ans=0;
	for (int k=1;k<=n;++k)
	{
		for (int j=1;j<=m;++j)
		{
			sum[j]=sum[j-1]+(map[k][j]=='.');
			for (int i=1;i<=j;++i)
			{
				if (high[i][j])
				{
					if (map[k][i]=='.'&&map[k][j]=='.')
						high[i][j]+=1;
					else 
						high[i][j]=0;
				} 
				
				if (sum[j]-sum[i-1]==j-i+1)
				{
					if (high[i][j]==0)
						high[i][j]=1;
					ans=max(ans,high[i][j]*(j-i+1));
				}
			}
		}
	}
	cout<<ans<<endl;
}
int main()
{
	freopen("fortmoo.in","r",stdin);
	freopen("fortmoo.out","w",stdout);
	init();
	solve();
	return 0;
}