// 以下为DFS代码

#include<iostream>
#include<algorithm>
#include<vector>
#include<map>
using namespace std;
const int MAXN = 305;
char mp[MAXN][MAXN];
bool vis[MAXN][MAXN];
int dist[MAXN][MAXN];
int n, m, ans = 100000;
int sx, sy, endx, endy;
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
struct Portal{
	int x1, y1;
	int x2, y2;
};
struct coord{
	int x, y;
	bool operator<(const coord& other) const {
        if (x != other.x) return x < other.x;
        return y < other.y;
    }
};
map<char, Portal> _ptls;
map<coord, coord> ptls;
bool is_letter(int x, int y){
	return mp[x][y] >= 'A' && mp[x][y] <= 'Z';
}
void dfs(int x, int y, int cnt){
	if (dist[x][y] && cnt >= dist[x][y]) return;
	else dist[x][y] = cnt;
	// cout << x << " " << y << " " << mp[x][y] << endl;
//	if (mp[x][y] == '=') {ans = min(cnt, ans); return;}
	for (int k = 0; k < 4; k++){
		int nx = x + dx[k], ny = y + dy[k];
		// cout << nx << " " << ny << " " << mp[nx][ny] << endl;
		if (nx >= 1 && ny >= 1 && nx <= n && ny <= m
			&& mp[nx][ny] != '#' && mp[nx][ny] != '@'){
			// cout << nx << " " << ny << " " << mp[nx][ny] << endl;
			char nt = mp[nx][ny];
			if (nt == '.' && !vis[nx][ny]) {
				vis[nx][ny] = true;
				dfs(nx, ny, cnt + 1);
				vis[nx][ny] = false;
			}
			if (nt == '='){
				ans = min(ans, cnt + 1);
				continue;
			}
			if (is_letter(nx, ny)){
				coord p = ptls[{nx, ny}];
				if (vis[p.x][p.y]) continue;
				vis[p.x][p.y] = true;
				dfs(p.x, p.y, cnt + 1);
				vis[p.x][p.y] = false;
			}
		}
	}
}
int main(){
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++){
			cin >> mp[i][j];
			if (mp[i][j] >= 'A' && mp[i][j] <= 'Z'){
				if (_ptls.find(mp[i][j]) == _ptls.end()) _ptls[mp[i][j]].x1 = i, _ptls[mp[i][j]].y1 = j;
				else _ptls[mp[i][j]].x2 = i, _ptls[mp[i][j]].y2 = j;
			}
			else if(mp[i][j] == '@')
				sx = i, sy = j;
		}
	for (auto pt : _ptls){
		coord p1, p2;
		p1.x = pt.second.x1, p1.y = pt.second.y1;
		p2.x = pt.second.x2, p2.y = pt.second.y2;
		ptls[p1] = p2;
		ptls[p2] = p1;
	}
	dfs(sx, sy, 0);
	cout << ans;
}


// 以下为BFS代码

void bfs(int sx, int sy) {
    queue<coord> q;
    q.push({sx, sy});
    vis[sx][sy] = true;
    dist[sx][sy] = 0;
    while (!q.empty()) {
        coord u = q.front();
        q.pop();
        for (int k = 0; k < 4; k++) {
            int nx = u.x + dx[k];
            int ny = u.y + dy[k];
            if (nx < 1 || ny < 1 || nx > n || ny > m)
                continue;
            char nt = mp[nx][ny];
            if (nt == '#' || nt == '@')
                continue;
            if (nt == '=') {
                ans = dist[u.x][u.y] + 1;
                return;
            }
            coord p = {nx, ny};
            if (is_letter(nx, ny))
                p = ptls[p];
            if (vis[p.x][p.y])
                continue;
            vis[p.x][p.y] = true;
            dist[p.x][p.y] = dist[u.x][u.y] + 1;
            q.push(p);
        }
    }
}