#include <iostream>
#define IN(x,s,g) ((x) >= (s) && (x) < (g))
#define ISIN(x,y,w,h) (IN((x),0,(w)) && IN((y),0,(h)))

#include <cstring>
#include <queue>
#define REP(i,n) for(int i=0; i<(int)(n); i++)

#include <cstdio>
inline int getInt(){ int s; scanf("%d", &s); return s; }

#include <set>

using namespace std;

int d[3010][3010];
char g[3010][3010];

inline int get(int x, int y, int w, int h) {
  return ISIN(x, y, w, h) ? d[y][x] : 0;
}

int main(){
  const int h = getInt();
  const int w = getInt();
  REP(i,h) scanf("%s", g[i]);

  int ans = 0;
  REP(i,h) REP(j,w) {
    if (g[i][j] == '.') d[i][j] = 0;
    else d[i][j] = min(get(j - 1, i, w, h),
		       min(get(j, i - 1, w, h),
			   get(j - 1, i - 1, w, h))) + 1;
    ans = max(ans, d[i][j]);
  }

  // REP(i,h) { REP(j,w) printf("%02d ", d[i][j]); puts(""); }

  printf("%d\n", (ans + 1) / 2);
  return 0;
}