#include<stdio.h>
int main(){
    int n;
    scanf("5d", &n);
    if (n < 0){
        printf("Invalid input\n");
    } else{
        long long factorial = 1;
        for (int i; i <= n; i++){
            factorial *= i;
        }
        printf("%lld\n", factorial);
    }
    return 0;
}