#include <cstdio>
#include <algorithm>

using namespace std;

#define MAX_N 101

char s[MAX_N][MAX_N];
int d[MAX_N][MAX_N];

int main() {
    int n, m;
    scanf( "%d%d", &n, &m );
    for ( int i = 1; i <= n; ++i )
        gets( s[i] + 1 );

    for ( int i = 1; i <= n; ++i )
        for ( int j = 1; j <= m; ++j )
            if ( s[i][j] == '.' )
                d[i][j] = max( d[i - 1][j] + 1, d[i][j - 1] + 1 );

    int ans = 0;
    for ( int i = 1; i <= n; ++i )
        for ( int j = 1; j <= m; ++j )
            ans = max( ans, d[i][j] );

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