#include <bits/stdc++.h>
using namespace std;
int num[60];
int main() {
  int n;
  while (~scanf("%d", &n)) {
    for (int i = 0; i < n; i++) scanf("%d", &num[i]);
    sort(num, num + n);
    int tmp = 1;
    for (int i = 0; i < n - 1; i++) {
      if (num[i] == num[i + 1]) continue;
      if (num[i] + 1 == num[i + 1]) {
        tmp++;
        if (tmp == 3) break;
      } else
        tmp = 1;
    }
    if (tmp == 3)
      printf("YES\n");
    else
      printf("NO\n");
  }
  return 0;
}
