#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  vector<int> v(4);
  for (int i = 0; i < 4; i++) cin >> v[i];
  sort(v.begin(), v.end());
  for (int i = 0; i < 3; i++) {
    if (v[i+1] - v[i] != 1) {
      cout << "No" << "\n";
      return 0;
    }
  }
  cout << "Yes" << "\n";
}