#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int n;
  string s;
  cin>>n>>s;
  for(Int i=1;i<n;i++) if(s[i-1]==s[i]) return cout<<"YES"<<endl,0;
  cout<<(n>=4?"YES":"NO")<<endl;
  return 0;
}