#include <bits/stdc++.h>
using namespace std;
int a[1011];
int n, i, ans, x;
bool cmp(int a, int b) { return a < b; }
int main() {
  scanf("%d", &n);
  memset(a, 0, sizeof(a));
  for (i = 0; i < n; ++i) {
    scanf("%d", &x);
    a[x] = 1;
  }
  ans = 0;
  for (i = 1; i < 1001; ++i)
    if (a[i] + a[i + 1] + a[i + 2] == 3) {
      ans = 1;
      break;
    }
  if (ans == 1) {
    printf("YES\n");
  } else {
    printf("NO\n");
  }
  return 0;
}
