#include <cstdio>
#include <vector>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <sstream>
#include <cmath>
#include <climits>
#include <set>
#include <iostream>
#include <map>
#include <functional>
#include <cstdlib>
#include <numeric>
#include <queue>
#include <complex>
#include <sstream>
#include <stack>

using namespace std;

#define reep(i,f,n) for(int i=f; i<int(n); ++i)
#define rep(i,n) reep(i,0,n)

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef complex<double> Point;

int main()
{
	int h, w;
	while(scanf("%d%d", &h, &w), h){
		int ans = 0;
		int tmp[512] = {0};
		rep(i, h){
			char field[512];
			scanf("%s", field);
			field[w] = '*';
			
			stack<pii> S;
			rep(j, w+1){
				tmp[j] = field[j] == '*' ? 0 : tmp[j]+1;
				pii rect(tmp[j], j);
				if(S.empty())
					S.push(rect);
				else{
					if(S.top().first < rect.first)
						S.push(rect);
					else if(S.top().first > rect.first){
						int target = j;
						while(!S.empty() && S.top().first >= rect.first){
							pii pre = S.top();
							S.pop();
							ans = max(ans, pre.first*(j-pre.second));
							target = pre.second;
						}
						rect.second = target;
						S.push(rect);
					}
				}
			}
		}

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

	return 0;
}