#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;
int n,m,xn[5]={0,-1,0,1,0},yn[5]={0,0,1,0,-1},endx,endy,vis[310][310];
char c[310][310];
bool b[310][310];
queue <pair<int,int> > q;
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>c[i][j]; 
			if(c[i][j]=='@'){
				q.push(make_pair(i,j));
				b[i][j]=1;
			} 
			if(c[i][j]=='='){
				endx=i;
				endy=j;
			} 
		} 
	}
	while(!q.empty()){
		pair <int,int> p=q.front();
		q.pop();
		for(int i=1;i<=4;i++){
			int ex=p.first+xn[i];
			int ey=p.second+yn[i];
			if(c[ex][ey]>='A'&&c[ex][ey]<='Z'){
				for(int j=1;j<=n;j++){
					for(int k=1;k<=m;k++){
						if(j!=ex&&k!=ey&&c[j][k]==c[ex][ey]){
							b[ex][ey]=1;
							b[j][k]=1;
							q.push(make_pair(j,k));
							vis[j][k]=vis[p.first][p.second]+1;
						}
					}
				}
			}
			else if(!b[ex][ey]&&ex>=1&&ex<=n&&ey>=1&&ey<=m&&c[ex][ey]!='#'){
				q.push(make_pair(ex,ey));
				b[ex][ey]=1;
				vis[ex][ey]=vis[p.first][p.second]+1;
			} 
		}
	}
    cout<<vis[endx][endy];
	return 0;
}