import java.util.*;
import java.io.*;
import java.awt.geom.*;
import java.math.*;

public class No0290 {

	static final Scanner in = new Scanner(System.in);
	static final PrintWriter out = new PrintWriter(System.out,false);

	static void solve() {
		int n = in.nextInt();
		String s = in.next();
		boolean f = false;
		for (int i=0; i<n; i++) {
			if (i + 1 < n && s.charAt(i) == s.charAt(i+1)) f = true;
			if (i + 3 < n && s.charAt(i) == s.charAt(i+2) && s.charAt(i+1) == s.charAt(i+3)) f = true;
		}
		out.println(f ? "YES" : "NO");
	}

	public static void main(String[] args) {
		long start = System.currentTimeMillis();

		solve();
		out.flush();

		long end = System.currentTimeMillis();
		//trace(end-start + "ms");
		in.close();
		out.close();
	}

	static void trace(Object... o) { System.out.println(Arrays.deepToString(o));}
}