#include <iostream>
using namespace std;

long long factorial(int n);

int main() {

    int n;
    cin >> n;

    cout << factorial(n) << endl;

    return 0;
}

long long factorial(int n) {

    // write your code here......
    return n > 1 ? n * factorial(n - 1) : 1;//用三目操作符进行处理
}