#include <cstdio>

#define N 201

#define max(x, y) ((x) > (y) ? (x) : (y))

int n, m, ans, p;

int h[N][N], b[N];

char s[N][N];

int main()

{

	int i, j, k;

	scanf("%d %d", &n, &m);

	for(i = 1; i <= n; i++)

	{

		scanf("%s", s[i] + 1);

		for(j = 1; j <= m; j++)

			if(s[i][j] == '.')

				h[i][j] = h[i - 1][j] + 1;

	}

	for(i = 1; i <= n; i++)

		for(j = i + 1; j <= n; j++)

		{

			p = -1;

			for(k = 1; k <= m; k++) b[k] = h[j][k];

			for(k = 1; k <= m; k++)

				if(s[i][k] == 'X')

					b[k] = 0;

			for(k = 1; k <= m; k++)

			{

				if(!b[k]) p = -1;

				if(j - b[k] < i && p == -1) p = k;

				if(j - b[k] < i && p != -1) ans = max(ans, (k - p + 1) * (j - i + 1));

			}

		}

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

	return 0;

}