#include <bits/stdc++.h>
using namespace std;
int a[55];
int main() {
  int n, flag = 0;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", &a[i]);
  sort(a, a + n);
  int t = unique(a, a + n) - a;
  for (int i = 0; i < t - 2; i++) {
    if (a[i] == a[i + 1] - 1 && a[i + 2] - 2 == a[i]) {
      flag = 1;
      break;
    }
  }
  if (flag)
    printf("YES\n");
  else
    printf("NO\n");
  return 0;
}
