OI-codes/Luogu/problem/P1134/P1134.cpp

#include <bits/stdc++.h>

using namespace std;

int n, ans = 1, a[] = {6, 8, 4, 2};

int main() {
    cin >> n;
    while (n) {
        for (int i = 1; i <= n % 10; i++) {
            if (i != 5) {
                ans = ans * i % 10;
            }
        }
        n = n / 5;
        ans = ans * a[n % 4] % 10;
    }
    cout << ans << endl;
    return 0;
}