int factorial (int n) {
    if(n==0) return 1;
    return n*factorial(n-1);
}
int main (){
    int n;
    scanf("%d",&n);
    
    if(n<0 ||n>10){
        printf("invalid input\n");
    }else{
        print("%d\n",factorial(n));
        
    }    
    
    return 0;
}