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

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