末位数的，100%

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;

    cin >> n;

    long long sum = 1;

    for (int i = 1; i <= n; ++i) {
        sum *= i;
        while (0 == (sum % 10)) {
            sum = sum / 10;
        }
        if (sum > 100000000) {
            sum = sum % 100000000;
        }
    }

    if (0 == n) {
        sum = 0;
    }
    cout << sum % 10 << endl;
}