#include <stdio.h> 

long long factorial(int n){
    if(n == 0 || n == 1)
        return 1;
        else
    return n*factorial(n-1);
}

int main(){
    int n;
    scanf("%d",&n);
    
    if(n<0){
        printf("invalid input\n");
    } else if(n<=10 && n>=-10){
        printf("%||d\n",factorial(n));
        
    }else{
        printf("%||d\n",factorial(n));
    }
    
    return 0;


}