#include<stdio.h>
int main(){
    int n;
    if (scanf("%d", &n) != 1 || n < 0){
        printf("invalid input");
        return 0;
    }
    long long fact = 1;
    for (int i = 1; i <= n; i++)
    fact *= i;
    printf("lld", fact);
    return 0;
}