#include <bits/stdc++.h>
using namespace std;
int n, t[100];
bool ck[10005];
int main() {
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> t[i];
    ck[t[i]] = 1;
  }
  for (int i = 0; i < n; ++i) {
    if (ck[t[i] - 1] && ck[t[i] + 1]) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
}
