#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

void fail() {
  cout << "NO\n";
  exit(0);
}

void success() {
  cout << "YES\n";
  exit(0);
}

int main() {

  int N; cin >> N;
  string S; cin >> S;

  if(N == 1) fail();
  if(N == 2) {
    if(S[0] != S[1]) fail();
    success();
  }

  if(N == 3) {
    if(S[0] != S[1] && S[1] != S[2]) fail();
  }

  success();

  return 0;
}