package main

import (
	"fmt"
)

var (
	N int
)

func resolve() int {
	for i := N - 100; i <= N+100; i++ {
		if i != 2 && i%2 == 0 {
			return i
		}
	}
	return -1
}

func main() {
	fmt.Scanf("%d\n", &N)
	fmt.Println(resolve())
}