#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))


int dx[4] = { 1,-1, 0, 0};
int dy[4] = { 0, 0, 1,-1};

const int Max = 21;

int w,h;
char c[Max][Max];
bool f[Max][Max];

typedef pair<int,int> P;

char mark[2] = {'a','b'};

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

	queue<P> q;
	q.push( P(i,j) );

	while(!q.empty())
	{
		P now = q.front();q.pop();
		
		int x = now.first,y = now.second;

		f[x][y] = true;
		if(c[x][y] == mark[1])
		{
			return abs(x-i)+abs(y-j)-1;
		}

		for(int k = 0;k < 4;k++)
		{
			int tx = now.first+dx[k],ty = now.second+dy[k];

			if((tx >= 0 && ty >= 0 && tx < h && ty < w && !f[tx][ty]))
			{
				q.push(P(tx,ty));
			}
		}
	}
}

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++)
		{
			int tx = i+dx[k];int ty = j+dy[k];
			dfs(tx,ty,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++)
		{
			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];

	for(int i = 0;i < 2;i++)
	{
		CLR(f);
		cast(mark[i]);
	}

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

	cout << anser << endl;


	return 0;
}