#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int a[1005];
  while (scanf("%d", &n) != EOF) {
    int tmp;
    memset(a, 0, sizeof(a));
    for (int i = 0; i < n; i++) {
      scanf("%d", &tmp);
      a[tmp]++;
    }
    bool flag = false;
    for (int i = 0; i < 1000; i++) {
      if (a[i] && a[i + 1] && a[i + 2]) {
        flag = true;
        break;
      }
    }
    if (flag == true) {
      printf("YES\n");
    } else
      printf("NO\n");
  }
  return 0;
}
