#include <bits/stdc++.h>
using namespace std;
int a[55], b[55];
int main() {
  int n;
  while (scanf("%d", &n) != EOF) {
    int i, j;
    memset(a, 0, sizeof(a));
    memset(b, 0, sizeof(b));
    for (i = 0; i < n; i++) scanf("%d", &a[i]);
    sort(a, a + n);
    for (i = 0, j = 0; i < n; i++)
      if (a[i] != a[i + 1]) b[j++] = a[i];
    int flg = 0;
    sort(b, b + n);
    int k = 0;
    for (i = 0; i < n; i++)
      if (!b[i]) k++;
    for (i = k; i < n - 2; i++)
      if (b[i + 2] - b[i] <= 2) flg = 1;
    if (flg)
      printf("YES\n");
    else
      printf("NO\n");
  }
  return 0;
}
