#include<stdio.h>
long kaijo(int);
int main(void){
  long k,n;
  printf("Calculation of factorial.\n");
  printf("Give n : ");
  scanf("%ld",n);
  k=kaijo(n);
  printf("n! = %d\n",k);
  return 0;
}
long kaijo(int n){
    if (n>1) return n*kaijo(n-1);
    return 1;
}