#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>

using namespace std;

 
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define CLR(a) memset((a), 0 ,sizeof(a))
#define MCLR(a) memset((a), -1 ,sizeof(a))



//遷移数
const int TMAX = 4;

//遷移変数
int dx[TMAX][2] = {{ 1, 0},
				   {-1, 0},
				   { 0, 1},
				   { 0,-1},};


int w,h;
char c[21][21];



bool f[21][21];//フラグ CLR(f);

int dfs2(int i,int j)
{
	if(i < 0 || j < 0 || i >= h || j >= w || f[i][j])return 0;
	f[i][j] = true;

	if(c[i][j] == 'b')
	{
		return 1;
	}else
	if(c[i][j] != 'a')
	{
		int Max = 0;
		for(int k = 0;k < 4;k++)
		{
			int tmp = dfs2(i+dx[k][0],j+dx[k][1])+1;
			if(tmp)tmp++;
			Max = max(Max,tmp);
		}
		return Max;
	}
	return 0;
}

int dfs(int i,int j,char ma)
{
	if(i < 0 || j < 0 || i >= h || j >= w || f[i][j])return 0;
	f[i][j] = true;

	if(c[i][j] == '#')return 0;
	
	if(c[i][j] == '.')
	{
		for(int k = 0;k < 4;k++)
		dfs(i+dx[k][0],j+dx[k][1],ma);
		c[i][j] = ma;
		return 1;
	}
	return 0;
}

void cast(char ma)
{
	for(int i = 0;i < h;i++)
		for(int j = 0;j < w;j++)
		{
			CLR(f);
			if(dfs(i,j,ma))return;
		}
}


int main()
{

	cin >> w >> h;

	for(int i = 0;i < h;i++)
		for(int j = 0;j < w;j++)
			cin >> c[i][j];
	cast('a');
	cast('b');

	int anser = 99999999;
	for(int i = 0;i < h;i++)
		for(int j = 0;j < w;j++)
		{
			CLR(f);
			if(c[i][j] == 'a')
			anser = min(dfs2(i,j),anser);
		}

	cout << anser << endl;


	return 0;
}