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 (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>
#include <math.h>

int main (void){
	int X, ans, root, i;
	int flag =0; /*判定フラグ*/
	scanf("%d", &X);
	
	while(1){
		root = (int)sqrt(X);
		
		for (i =2; i<root; ++i){
			if(X%i==0){
				flag =1;
				break;
			}
		}
		
		if (flag == 0){
			ans = X;
			break;
		}
		flag =0;
		X +=1;
	}
	
	printf("%d", ans);
}