#include <bits/stdc++.h>
using namespace std;
int s[10001];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d", &s[i]);
  }
  sort(s, s + n);
  int len = unique(s, s + n) - s;
  int flog = 0;
  for (int i = 0; i < len; i++) {
    if (s[i + 1] == s[i] + 1 && s[i + 2] == s[i + 1] + 1) {
      flog = 1;
      break;
    }
  }
  if (flog == 1)
    printf("YES\n");
  else
    printf("NO\n");
  return 0;
}
