import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


int N;
string S;

bool solve() {
  if (N >= 4) {
    return true;
  } else {
    foreach (k; 1 .. N + 1) {
      foreach (i; 0 .. N + 1 - 2 * k) {
        if (S[i .. i + k] == S[i + k .. i + 2 * k]) {
          return true;
        }
      }
    }
    return false;
  }
}

void main() {
  try {
    for (; ; ) {
      N = readInt();
      S = readToken();
      const ans = solve();
      writeln(ans ? "YES" : "NO");
    }
  } catch (EOFException e) {
  }
}