package main

import (
	"fmt"
	"math"
)

func main() {
	var h, w int
	fmt.Scanf("%d %d", &h, &w)

	dp := [][]int{}
	for i := 0; i <= h; i++ {
		dp = append(dp, make([]int, w+1))
	}

	max := 0
	for y := 1; y <= h; y++ {
		var row string
		fmt.Scanf("%s", &row)
		for x := 1; x <= w; x++ {
			if row[x-1:x] == "." {
				continue
			}
			dp[y][x] = minInt(dp[y-1][x-1], dp[y-1][x], dp[y][x-1]) + 1
			max = maxInt(max, dp[y][x])
		}
	}
	fmt.Println((max + 1) / 2)
}

func maxInt(list ...int) int {
	max := int(math.MinInt64)
	for _, i := range list {
		if i > max {
			max = i
		}
	}
	return max
}

func minInt(list ...int) int {
	min := int(math.MaxInt64)
	for _, i := range list {
		if i < min {
			min = i
		}
	}
	return min
}