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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	nextReader = newScanner()
	x := nextInt()
	for !isPrime(x) {
		x++
	}
	fmt.Println(x)
}

func isPrime(n int) bool {
	if n < 2 {
		return false
	}
	for i := 2; i*i <= n; i++ {
		if n%i == 0 {
			return false
		}
	}
	return true
}

// ---------------------------------------------------------------
// I/O
// ---------------------------------------------------------------
var nextReader func() string

func newScanner() func() string {
	sc := bufio.NewScanner(os.Stdin)
	sc.Buffer(make([]byte, 1024), int(1e11))
	sc.Split(bufio.ScanWords)
	return func() string {
		sc.Scan()
		return sc.Text()
	}
}

func nextString() string { return nextReader() }

func nextInt() int { n, _ := strconv.Atoi(nextReader()); return n }

func nextInts(size int) []int {
	ns := make([]int, size)
	for i := 0; i < size; i++ {
		ns[i] = nextInt()
	}
	return ns
}