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