//om namah shivaaay//
#include <bits/stdc++.h>
#define Om_namah_Shivaay ios::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)
#define ll long long
 using namespace std;
 int main()
 {
	 Om_namah_Shivaay;
	 int a,b,c,d;
	 cin>>a>>b>>c>>d;
	 
    vector<int> arr;
   arr.push_back(a);
    arr.push_back(b);
    arr.push_back(c);
    arr.push_back(d);
     sort(arr.begin(),arr.end());
    
    if(arr[1]==arr[0]+1 &&arr[2]==arr[1]+1&&arr[3]==arr[2]+1)
    {
		cout<<"Yes"<<endl;
       }
       else{
		   cout<<"No"<<endl;
		   }
}