package main

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

func main() {
	sc.Split(bufio.ScanWords)
	n := nextInt()
	s := nextLine()
	ans := false
	for i := 0; i <= n; i++ {
		for j := i + 1; j+j-i <= n; j++ {
			//fmt.Println(i, j)
			if s[i:j] == s[j:j+j-i] {
				ans = true
				j = n
				i = n
			}
		}
	}
	if ans {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}


var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
    sc.Scan()
    return sc.Text()
}

func nextInt() int {
    i, _ := strconv.Atoi(nextLine())
    return i
}