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>

char kugyu[1234567] = {1, 1};

int main(void) {
	int i, j;
	int X;
	int tomatu;
	for (i = 2; i < 1234567; i++) {
		if (!kugyu[i]) {
			for (j = i * 2; j < 1234567; j += i) {
				kugyu[j] = 1;
			}
		}
	}
	if (scanf("%d", &X) != 1) return 1;
	for (tomatu = X; tomatu < 1234567; tomatu++) {
		if (!kugyu[tomatu]) {
			printf("%d\n", tomatu);
			return 0;
		}
	}
	puts("error");
	return 0;
}