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>

int isPrime(int n){
    if(n==1){
        return 0;
    }
    if(n==2||n==3){
        return 1;
    }
    if(n%2==0||n%3==0){
        return 0;
    }
    for(int i=5;i*i<=n;i+=2){
        if(i%3==0){
            continue;
        }
        if(n%i==0){
            return 0;
        }
    }
    return 1;
}

int main(){
    int x;
    scanf("%d", &x);
    if(x>2 && x%2==0){
        x++;
    }
    while(!isPrime(x)){
        x++;
    }
    printf("%d", x);

    return 0;
}