#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1e9;
int MOD = 1e9+7;
int dist[3000][3000];
char S[3000][3000];
int H,W;
main(){
    cin >> H >> W;
    for(int i = 0;i < H;i++){
        cin >> S[i];
    }
    int dx[] = {-1, 0, -1};
    int dy[] = {-1,-1, 0};
    int maxi = 0;
    for(int i = 0;i < H;i++){
        for(int j = 0;j < W;j++){
            if(S[i][j] == '.')continue;
            if(i == 0 || j == 0){
                dist[i][j] = 1;
                continue;
            }
            int mini = INF;
            for(int k = 0;k < 3;k++)if(j+dx[k] < W && i+dy[k] < H)mini = min(mini,dist[ i+dy[k] ][ j+dx[k] ]);
            dist[i][j] = mini + 1;
            maxi = max(maxi,mini+1);
        }
    }
    cout << (maxi+1)/2 << endl;
}