// yukicoder: No.402 最も海から遠い場所
// 2019.7.19 bal4u

#include <stdio.h>

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

void ins(char *s) { // 文字列の入力　スペース以下の文字で入力終了
	do *s = gc();
	while (*s++ > ' ');
}

int H, W;
int dp[3005][3005];
char map[3005][3005];

int largestSquare() {
	int r, c, ans = 0;
	for (r = 1; r <= H; r++) for (c = 1; c <= W; c++) {
		if (map[r][c] == '.') dp[r][c] = 0;
		else {
			int t = dp[r-1][c-1];
			if (t > 0 && dp[r  ][c-1] < t) t = dp[r  ][c-1];
			if (t > 0 && dp[r-1][c  ] < t) t = dp[r-1][c  ];
			dp[r][c] = t+1;
		}
	}
	return ans;
}

int main()
{
	int r, c, ans;

	H = in(), W = in();
	for (r = 1; r <= H; r++) ins(map[r]+1);
	largestSquare();
	ans = 0;
	for (r = 1; r <= H; r++) for (c = 1; c <= W; c++) {
		if (dp[r][c] > ans) ans = dp[r][c];
	}
	printf("%d\n", (ans+1)>>1);
	return 0;
}