#include <bits/stdc++.h>

using namespace std;

int main() {
  vector<int> v(4);
  cin >> v[0] >> v[1] >> v[2] >> v[3];
  sort(v.begin(), v.end());
  if (v[0] + 1 == v[1] && v[1] + 1 == v[2] && v[2] + 1 == v[3]) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }

  return 0;
}