import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class N290
{
	public static void main(String[] args) throws IOException
	{
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		int l=Integer.parseInt(br.readLine());
		String str=br.readLine();
		int end=0;
		for(int i=1;end==0&&i<=l;i++)
		{
			for(int j=i;end==0&&j+1<=l&&j+(j+1-i)<=l;j++)
			{
				if(str.substring(i-1, j).equals(str.substring(j,j+(j+1-i))))
				{end++;}
			}
		}
		if(end==1){System.out.println("YES");}
		else{System.out.println("NO");}
	}

}