#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
int a[N];
bool vis[N];
int main() {
  int n, t;
  cin >> n;
  int pos = 0;
  memset(vis, 0, sizeof(vis));
  for (int i = 0; i < n; i++) {
    cin >> t;
    if (!vis[t]) {
      a[pos++] = t;
      vis[t] = 1;
    }
  }
  sort(a, a + pos);
  bool flag = 0;
  for (int i = 1; i < pos - 1; i++) {
    if (a[i] == a[i - 1] + 1 && a[i] == a[i + 1] - 1) {
      flag = 1;
    }
  }
  if (flag)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
