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;
bool isPrime(int n) // assuming n > 1
{
    int i,root;
if(n==2||n==3)
    return true;
if(n==1)
    return false;
    if (n%2 == 0 || n%3 == 0)
        return false;

    root = (int)sqrt(n);

    for (i=5; i<=root; i+=6)
    {
        if (n%i == 0)
           return false;
    }

    for (i=7; i<=root; i+=6)
    {
        if (n%i == 0)
           return false;
    }

    return true;
}
int main()
{
int a;
cin>>a;
while(!isPrime(a))
++a;
cout<<a;
return 0;
}