#include<iostream>
using namespace std;
#include<queue>
struct coord
{
	int x, y, step;
};
struct f
{
	int x1, y1, x2, y2;
}mark[100];
queue<coord>Q;
int n, m, wk[4][2] = { {0,1},{0,-1},{1,0},{-1,0} };
char a[305][305], t;
int main()
{
	cin >> n >> m;
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			cin >> t;
			a[i][j] = t;
			if (t == '@')
			{
				a[i][j] = '#';
				Q.push({ i,j,0 });
			}
			else if (isalpha(t))
			{
				if (mark[t].x1 == 0) mark[t].x1 = i, mark[t].y1 = j;
				else mark[t].x2 = i, mark[t].y2 = j;
			}
		}
	}
	while (!Q.empty())
	{
		coord u = Q.front();
		Q.pop();
		for (int i = 0; i < 4; i++)
		{
			int x = u.x + wk[i][0], y = u.y + wk[i][1];
			if (x < 0 || x >= n || y < 0 || y >= n || a[x][y] == '#') continue;
			if (a[x][y] == '.')
			{
				a[x][y] = '#';
				Q.push({ x,y,u.step + 1 });
				continue;
			}
			if (a[x][y] == '=')
			{
				cout << u.step + 1;
				return 0;
			}
			if (x == mark[a[x][y]].x1 && y == mark[a[x][y]].y1) Q.push({ mark[a[x][y]].x2,mark[a[x][y]].y2,u.step + 1 });
			else Q.push({ mark[a[x][y]].x1,mark[a[x][y]].y1,u.step + 1 });
		}
	}
	return 0;
}