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<iostream>
#define maxn 10000010
using namespace std;
int ss[maxn];
int x;
int main(){
	cin >> x;
    ss[1] = 1;
    for(int i = 2; i*i <= 100000; ++i){
        if(!ss[i])
            for(int j = 2*i; j <= 1000000; j += i)
                ss[j] = 1;
    }
    for(int i = x; i <= 1000000; ++i){
    	if(!ss[i]){cout << i << endl;return 0;}
	}
    return 0;
}