#include <stdio.h>
long long factorial(int n) {
    if (n == 0) {
        return 1;
    } else {
      return (long long)n * factorial(n - 1);
    }
}
int main() {
    int num;
    scanf("%d", &num);
    
    if (num < 0) {
        printf("Invalid Input\n");
    } else {
      long long result = factorial(num);
      printf("%lid\n",result);
    }
    return 0;
}