gistfile1.c

#include <stdio.h>


int main () {

  int num;

  scanf("%d", &num);

  if (num <= 0) {
    return -1;
  }

  for (int divisor = 0; divisor <= num / 2; divisor ++) {
    if (num % divisor == 0) {
      printf("%s\n", "NO");
      return 0;
    }
  }


  printf("%s\n", "YES");
  return 0;
}