#include <bits/stdc++.h>
using namespace std;
int main() {
  int f, n, a[55];
  while (scanf("%d", &n) != EOF) {
    bool u = 0;
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    sort(a, a + n);
    f = 0;
    for (int i = 0; i < n - 1; i++)
      if (a[i] == a[i + 1]) a[i] = 0, f++;
    sort(a, a + n);
    for (int i = 1 + f; i < n - 1; i++)
      if (a[i] == a[i - 1] + 1 && a[i] + 1 == a[i + 1]) {
        u = true;
        break;
      }
    printf("%s\n", u ? "YES" : "NO");
  }
  return 0;
}
