#include<bits/stdc++.h>
using namespace std;
int n, m, a, b, c, d;
char g[305][305];
typedef pair<int, int>PII;
queue<PII>q;
int dist[305][305];
int st[305][305];
int dx[] = { 0,0,-1,1 };
int dy[] = { 1,-1,0,0 };
int bfs(int x, int y) {
    dist[x][y] = 0;
    q.push({ x,y });
     st[x][y] = 1;
    while (q.size()) {
        auto t = q.front();
        q.pop();
        if (g[t.first][t.second] >= 'A' && g[t.first][t.second] <= 'Z') {
            for (int i = 1; i <= n; i++) {
                for (int j = 1; j <= m; j++) {
                    if (i == t.first && t.second == j) continue;
                    if (g[t.first][t.second] == g[i][j]) {
                        t.first = i;
                        t.second = j;
                        break;
                    }

                }
            }
        }
        for (int i = 0; i < 4; i++) {
            int e = t.first + dx[i];
            int f = t.second + dy[i];
            if (e<1 || e>n || f<1 || f>m) continue;
            if (dist[e][f] >= 0) continue;
            if (g[e][f] == '#')continue;
             if (st[e][f] == 1) continue;
            q.push({ e,f });
             st[e][f] == 1;
            dist[e][f] = dist[t.first][t.second] + 1;
            if (g[e][f] == '=')return dist[e][f];
        }
    }return -1;
}
int main() {
    cin >> n >> m;
    memset(dist, -1, sizeof dist);
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            cin >> g[i][j];
            if (g[i][j] == '@') {
                c = i;
                d = j;
            }
        }
    }int res = bfs(c, d);
   // for (int i = 1; i <= m; i++)
     //   cout << dist[2][i];
    cout << res;
    return 0;
}