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

template<typename T>
void fin(T a){
  cout<<a<<endl;
  exit(0);
}

signed main(){
  int n;string s;cin>>n>>s;
  if(n==1)fin("NO");
  if(n==2&&s[0]!=s[1])fin("NO");
  if(n==3&&s[0]!=s[1]&&s[1]!=s[2])fin("NO");
  fin("YES");
}