#include <iostream>

using namespace std;

int main() {
	int n,m,i,j,v[110][110],r = 0;
	char c;
	
	cin>>n>>m;

	for (i=1;i<=105;i++) {
		v[0][i] = 0;
		v[i][0] = 0;
	}
	
	for (i=1;i<=n;i++) {
		for (j=1;j<=m;j++) {
			cin>>c;
			if (c == '.') {
				if ((v[i-1][j] == 0) && (v[i][j-1] == 0)) {
					v[i][j] = 0;
					if (i == 1 && j == 1) v[i][j] = 1;
				} else {
					v[i][j] = max(v[i-1][j], v[i][j-1]) + 1;
				}
				if (r < v[i][j]) r = v[i][j];
			} else v[i][j] = 0;
		}
	}
	
	cout<<r;
	
	return 0;
}