#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int MAXN = 35, MAXM = 1e5 + 5;
char mp[MAXN][MAXN];
int n, m, dis[MAXN][MAXN][MAXN][MAXN];
int dx[5] = { 0, 1, 0, -1 }, dy[5] = { 1, 0, -1, 0 };
struct node {
    int xx, yy;
    node() {}
    node(int xxx, int yyy) {
        xx = xxx;
        yy = yyy;
    }
};
void bfs(int x, int y) {
    queue<node> q;
    q.push(node(x, y));
    memset(dis[x][y], 0x3f, sizeof(dis[x][y]));
    dis[x][y][x][y] = 0;
    while (!q.empty()) {
        int xx = q.front().xx, yy = q.front().yy;
        q.pop();
        for (int i = 0; i < 4; i++) {
            int xxx = xx + dx[i], yyy = yy + dy[i];
            if (xxx > n || yyy > m || xxx < 1 || yyy < 1 || mp[xxx][yyy] == '#')
                continue;
            if (dis[x][y][xxx][yyy] > dis[x][y][xx][yy] + 1) {
                dis[x][y][xxx][yyy] = dis[x][y][xx][yy] + 1;
                q.push(node(xxx, yyy));
            }
        }
    }
}
int cnt, X[MAXN], Y[MAXN];
int dp[MAXM][MAXN];
int main() {
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            cin >> mp[i][j];
            if (mp[i][j] == 'p')
                X[0] = i, Y[0] = j;
            if (mp[i][j] == '@')
                X[++cnt] = i, Y[cnt] = j;
        }
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (mp[i][j] == 'p' || mp[i][j] == '@')
                bfs(i, j);
        }
    }
    memset(dp, 0x3f, sizeof(dp));
    dp[0][0] = 0;
    for (int i = 0; i < cnt; i++) dp[1 << i][i + 1] = dis[X[0]][Y[0]][X[i + 1]][Y[i + 1]];
    for (int i = 1; i < (1 << cnt); i++) {
        for (int j = 0; j < cnt; j++) {
            if (!(i & (1 << j)))
                continue;
            for (int k = 0; k < cnt; k++) {
                int tmp = (1 << k);
                if (i & tmp)
                    continue;
                dp[i | tmp][k + 1] =
                    min(dp[i | tmp][k + 1], dp[i][j + 1] + dis[X[j + 1]][Y[j + 1]][X[k + 1]][Y[k + 1]]);
            }
        }
    }
    int ans = 0x3f3f3f3f;
    for (int i = 1; i <= cnt; i++) ans = min(ans, dp[(1 << cnt) - 1][i]);
    if (ans == 0x3f3f3f3f)
        puts("-1");
    else
        printf("%lld", ans);
    return 0;
}