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>
#include<math.h>

int pn(int x, int sqrtX){
    int i;
    for(i = 3; i <= sqrtX; i = i + 2){
        if(x % i == 0){
            return 0;
        }
    }

    return 1;
}

int main(){
    int x;
    int sqrtX;
    int i;
    int flag = 0;

    scanf("%d", &x);

    if(x != 2){
        while(1){
            sqrtX = sqrt(x);

            if(x % 2 != 0){
                flag = pn(x, sqrtX);
            }

            if(flag == 1){
                printf("%d", x);
                break;
            }else{
                x++;
            }
        }
    }else{
        printf("%d", x);
    }
    return 0;
}