#include<bits/stdc++.h>
using namespace std;
int n,m;
const int N = 310;
char g[N][N];//用于存地图的
int dist[N][N];//用于存起点到(i,j)的距离
bool vis[N][N];//记录这个点是否被访问过
typedef pair<int,int> PII;
int ansx,ansy,bx,by;
#define x first 
#define y second
queue <PII> q;
int dx[] = {-1,0,1,0};
int dy[] = {0,1,0,-1}; 
int bfs(int x1,int y1)
{
    memset(dist,-1,sizeof dist);
    memset(vis,false,sizeof vis);
    q.push({x1,y1});
    dist[x1][y1] = 0;
    vis[x1][y1] = true;
    
    while(!q.empty())
    {
        PII t = q.front();
        q.pop();
        
        for(int i=0;i<4;i++)
        {
            int a = t.x + dx[i];
            int b = t.y + dy[i];
            
            if(g[a][b] == '#')continue;
            if(vis[a][b] == true)continue;
            if(a>n||a<1||b<1||b>m)continue;
            
            vis[a][b] = true;
            dist[a][b] = dist[t.x][t.y] + 1; 
            
            if(g[a][b] == '=')return dist[a][b];
            
            else if(g[a][b] >= 'A'&&g[a][b] <= 'Z')
        	{
            	for(int i1=1;i1<=n;i1++)
                	for(int j=1;j<=m;j++)
                	{
                    	if(g[i1][j] == g[a][b] && (i1!=a||j!=b))
                    	{
                        	dist[i1][j] = dist[a][b]; //值先赋好
                        	
                        	q.push({i1,j});
                        
                    	}
                	}
            
        	}
            else q.push({a,b});
        }
        
        
    }
    //return dist[ansx][ansy];
}


int main()
{
    cin>>n>>m;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
        {
            cin>>g[i][j];
            if(g[i][j] == '@'){bx = i;by = j;}
            if(g[i][j] == '='){ansx = i;ansy = j;}
        }
    int res = bfs(bx,by);
    cout<<res<<endl;
//     for(int i=1;i<=n;i++)
//     {
// 		for(int j=1;j<=m;j++)cout<<dist[i][j]<<" ";
// 		cout<<endl;}
    return 0;
}