package main

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

var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readLine() string {
        buf := make([]byte, 0, 1000000)
        for {
                l, p, _ := rdr.ReadLine()
                buf = append(buf, l...)
                if !p {
                        break
                }
        }
        return string(buf)
}

func readStrings() []string {
        return strings.Split(readLine(), " ")
}

func readInts() (ret []int) {
        strings := readStrings()
        for i := range strings {
                num, _ := strconv.Atoi(strings[i])
                ret = append(ret, num)
        }
        return
}

func main() {
        readLine()
        S := readLine()
        for i := 0; i < len(S); i++ {
                for j := 1; j <= (len(S)-i)/2; j++ {
                        if S[i:i+j] == S[i+j:i+j+i+j-i] {
                                fmt.Println("YES")
                                os.Exit(0)
                        }
                }
        }
        fmt.Println("NO")
        os.Exit(0)
}