#include <bits/stdc++.h>
int n, m = 1;
int i, j, k;
int v[20000];
int can = 0;
int main() {
  scanf("%d", &n);
  for (i = 1; i <= n; i++) scanf("%d", &v[i]);
  std::sort(v + 1, v + 1 + n);
  for (i = 2; i <= n; i++)
    if (v[i] != v[i - 1]) v[++m] = v[i];
  for (i = 1; i + 2 <= m; i++)
    if (v[i + 2] - v[i] <= 2) can = 1;
  if (can)
    printf("YES");
  else
    printf("NO");
}
