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: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;

bool isprime(int x) {
    if (x % 2 == 0) return false;
    for (int a = 3; a < x; a+=2) {  //2ずつ増える a+=2; 3から始める
        // cout << x << a << endl;
        if (x % a == 0) return false;  //割り切れたらだめ
    }
    return true;    //最後に置く
}

int main () {
    int x;
    cin >> x;
    if (x == 2) {
        cout << 2 << endl;;
    }
    else if(x == 1) {
        cout << 1 << endl;
    }
    else {
        for (int j = x; j > 0; j++) {
            if(isprime(j)) {
                cout << j << endl;
                break;
            }
        }
    }
}