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

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  
  vector<int> x(4);
  for (int i = 0; i < 4; i++) cin >> x[i];
  
  sort(x.begin(), x.end());
  
  if (x[1] - x[0] == 1 && x[2] - x[1] == 1 && x[3] - x[2] == 1) cout << "Yes\n";
  else cout << "No\n";
}