#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr int MAX = 32;

int targetNum = 0;
char c[MAX][MAX];

const int dx[4] = { 1, 0, -1, 0 }, dy[4] = { 0, 1, 0, -1 };
int ansm = 1 << 30, ans = 0;
int distances[10][MAX][MAX];
bool isVisited[10][MAX][MAX];

void bfs(const pair<int, int> p, const int use) {
    // printf("(%d, %d) %d %d\n", p.first, p.second, ans, targetNum);

    //
    if (targetNum == 0 && ans != 0) {
        ansm = ans;
        return;
    }

    memset(isVisited[use], 0, sizeof(isVisited[use]));

    distances[use][p.first][p.second] = 0;
    isVisited[use][p.first][p.second] = true;

    queue<pair<int, int> > q;
    q.push(p);
    while (!q.empty()) {
        pair<int, int> p = q.front();
        q.pop();
        if (c[p.first][p.second] == '@') {
            ans += distances[use][p.first][p.second];
            c[p.first][p.second] = '.';
            --targetNum;
            bfs(p, use + 1);
            ans -= distances[use][p.first][p.second];
            c[p.first][p.second] = '@';
            ++targetNum;
        }
        for (int k = 0; k < 4; ++k) {
            int x = p.first + dx[k], y = p.second + dy[k];
            if (c[x][y] == '#' || isVisited[use][x][y])
                continue;
            isVisited[use][x][y] = true;
            distances[use][x][y] = distances[use][p.first][p.second] + 1;

            if (ans + distances[use][x][y] >= ansm)
                return;

            q.push(make_pair(x, y));
        }
    }
}

int main() {
    int n, m, i0, j0;
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= n; ++i) {
        scanf("\n");
        for (int j = 1; j <= m; ++j) {
            scanf("%c", &c[i][j]);
            switch (c[i][j]) {
                case '.':
                    break;
                case '@':
                    ++targetNum;
                    break;
                case 'p':
                    i0 = i;
                    j0 = j;
                    break;
            }
        }
    }
    for (int i = 0; i <= n + 1; ++i) c[i][0] = c[i][m + 1] = '#';
    for (int j = 0; j <= m + 1; ++j) c[0][j] = c[n + 1][j] = '#';

    /*for (int i = 0;i <= n + 1;++i) {
            for (int j = 0;j <= m + 1;++j) {
                    printf("%c", c[i][j]);
            }
            printf("\n");
    }*/

    pair<int, int> p = make_pair(i0, j0);

    bfs(p, 0);

    if (ansm == 1 << 30)
        ansm = -1;
    printf("%d", ansm);

    return 0;
}