#include <iostream>
#include <stdlib.h>
using namespace std;
void fail() {cout << "NO\n";exit(0);}
void success() {cout << "YES\n";exit(0);}
int main() {
  int N;string S;cin>>N>>S;
  if(N == 1 || (N == 2 && S[0] != S[1]) || (N == 3 && S[0] != S[1] && S[1] != S[2])) fail();
  success();
  return 0;
}