#include <bits/stdc++.h>
using namespace std;

int main() {
  vector<int> v(4);
  for (int i = 0; i < 4; i++) {
    cin >> v.at(i);
  }
  
  sort(v.begin(), v.end());
  int f = 0;
  for (int i = 0; i < 3; i++) {
    if (v.at(i) != v.at(i+1) - 1) f = 1;
  }
  
  if (!f) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }
}