#include <bits/stdc++.h>
#include <stdlib.h>
using namespace std;
int main(){
 vector<int> yon(4);
 for(int i= 0;i<4;i++){
   cin >> yon[i];
 }
sort(yon.begin(),yon.end());
if(yon[1]==yon[0]+1&&yon[2]==yon[1]+1&&yon[3]==yon[2]+1){
  cout << "Yes" << endl;
}else{
  cout << "No" << endl;
}
return 0;
}