#include <bits/stdc++.h>
using namespace std;
int q[1005];
int main() {
  int n, i, a;
  int f = 0;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> a;
    q[a]++;
  }
  for (i = 2; i < 1001; i++) {
    if (q[i - 2] && q[i - 1] && q[i]) f = 1;
  }
  if (f)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
