#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
using namespace std;
const int N = 1e5 + 10;
const int mod = 1e9 + 7;
const int inf = 0x3f3f3f3f;
int n, m, t;
int a[N];
int main() {
  int flag = 1;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  sort(a + 1, a + n + 1);
  for (int i = 2; i <= n; i++)
    if (a[i] != a[i - 1] + 1 || a[i] != a[i - 1]) {
      flag = 0;
      break;
    }
  if (flag)
    puts("Yes");
  else
    puts("No");
  return 0;
}
