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