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)

// ABC 149-C
// 2019.12.29 bal4u

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

int isprime(int a) {
	int i, b;
	if (a == 1) return 0;
	if (a == 2) return 1;
	if ((a & 1) == 0) return 0;
	b = (int)sqrt((double)a);
	for (i = 3; i <= b; i+=2) if (a % i == 0) return 0;
	return 1;
}

int main()
{
	int X;
	
	scanf("%d", &X);
	while (!isprime(X)) X++;
	printf("%d\n", X);
	return 0;
}