#include<iostream>
#include<algorithm>
#include<vector>

using namespace std;
using ll = long long;
int main(){
  vector<int> a(4);
  for (int i = 0; i < 4; i++){
    cin >> a[i];
  }
  sort(a.begin(), a.end());
  if(a[0] == a[1]-1 && a[1]== a[2]-1 && a[2] == a[3]-1){
    cout << "Yes\n";
  }else{
    cout << "No\n";
  }
  return 0;
}