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