#include<stdio.h>
#include<math.h>
int main() {
	int n = 0;
	while (scanf("%d", &n) != EOF) {
		if (n <= 1) {
			printf("no\n");
			continue;
		}
		int flag = 0;
		for (int i = 2; i <= sqrt(n); i++) {
			if (n % i == 0) {//不是素数
				flag = 1;
			}

		}
		if (flag == 0) {
			printf("yes\n");
		}
		else {
			printf("no\n");
		}
	}
	
	return 0;
}