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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define rep(i, n) for (int i = 2; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
#define m0(x) memset(x,0,sizeof(x))

bool is_prime(int a){
  int b = sqrt(a) + 1;
  rep(i, b+1){
    if(a%i == 0) return false;
  }
  return true;
}

int main(){
  int X;
  cin >> X;
  for(int i = 0;;i++){
    if(is_prime(X+i)){
      cout << X + i <<endl;
      break;
    }
  }
}