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

int main(void) {
	int  N,i,cnt;

	scanf("%d",&N);
	if(N==2) {printf("%d",N);return 0;}
	if(!(N%2)) N++;
	while(1) {
	  cnt=sqrt(N);
	  for(i=3;i<cnt;i+=2)
		  if(!(N%i)) break;
	  if(i>=cnt) break;
	  N+=2;
	}

    printf("%d",N);
    return 0;
}