package main

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

func main() {
	N := nextInt()
	S := next()

	if N >= 4 {
		fmt.Println("YES")
	}else {
		for ln := 1; ln <= N/2; ln++ {
			for i := 0; i < N-ln; i++ {
				if S[i:i+ln] == S[i+ln:i+2*ln] {
					fmt.Println("YES")
					return
				}
			}
		}
		fmt.Println("NO")

	}

}

var s = bufio.NewScanner(os.Stdin)

func next() string {
	s.Split(bufio.ScanWords)
	s.Scan()
	return s.Text()
}
func nextLine() string {
	s.Split(bufio.ScanLines)
	s.Scan()
	return s.Text()
}

func nextInt() int {
	i, e := strconv.Atoi(next())
	if e != nil {
		panic(e)
	}
	return i
}
func nextLong() int64 {
	i, e := strconv.ParseInt(next(), 10, 64)
	if e != nil {
		panic(e)
	}
	return i
}