#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, flag = 0, count = 1;
  cin >> n;
  vector<int> data(n, 0), ans;
  for (int i = 0; i < n; ++i) {
    cin >> data[i];
  }
  sort(data.begin(), data.end());
  for (int i = 1; i < data.size(); ++i) {
    if (data[i] - data[i - 1] != 0) {
      ans.push_back(data[i] - data[i - 1]);
    }
  }
  for (int i = 1; i < ans.size(); ++i) {
    if (ans[i] == 1 && ans[i - 1] == 1) {
      flag = 1;
      break;
    }
  }
  if (flag == 1) {
    cout << "YES\n";
  } else {
    cout << "NO\n";
  }
  return 0;
}
