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