#include <bits/stdc++.h>
using namespace std;

signed main(){
  int N; cin >> N;
  string S; cin >> S;
  if( S.size() >= 4 )
    cout << "YES" << endl, exit( 0 );
  for( int i = 1; i < S.size(); ++i )
    if( S[ i ] == S[ i - 1 ] ) 
      cout << "YES" << endl, exit( 0 );
  cout << "NO" << endl;
  return 0;
}