Problem:
Score: 300 points

Problem Statement

Find the minimum prime number greater than or equal to X.

Notes

A prime number is an integer greater than 1 that cannot be evenly divided by any positive integer except 1 and itself.

For example, 2, 3, and 5 are prime numbers, while 4 and 6 are not.

Constraints

2 \le X \le 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X

Output

Print the minimum prime number greater than or equal to X.

Sample Input 1

20

Sample Output 1

23

The minimum prime number greater than or equal to 20 is 23.

Sample Input 2

2

Sample Output 2

2

X itself can be a prime number.

Sample Input 3

99992

Sample Output 3

100003

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

// nが素数であれば1を、そうでなければ0を返す
int isprime(int n) {
	if(n < 2)
		return 0;
	int i;
	for(i = 2; i*i < n; i++)
		if(n%i == 0)
			return 0;
	return 1;
}

int main(void) {
	int x;
	scanf("%d", &x);
	while(1) {
		if(isprime(x)) {
			printf("%d\n", x);
			return 0;
		}
		x++;
	}
	return 0;
}