1#include <algorithm>2#include <cstdio>3#include <cstring>4bool flag[27];5int n;6int p[27];7int ans = 0;8void dfs(int k) {9    if (k == n + 1) {10        ++ans;11        return;12    }13    for (int i = 1; i <= n; ++i) {14        if (flag[i]) continue;15        if (k > 1 && i == p[k - 1] + 1) continue;16        p[k] = i;17        flag[i] = true;18        dfs(k + 1);19        flag[i] = false;20    }21    return;22}23int main() {24    scanf("%d", &n);25    dfs(1);26    printf("%d\n", ans);27    return 0;28}29