#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


template<typename T> void drop(const T &x){cout<<x<<endl;exit(0);}

//INSERT ABOVE HERE
signed main(){
  Int a,b,c,d;
  cin>>a>>b>>c>>d;
  vector<Int> vs({a,b,c,d});
  sort(vs.begin(),vs.end());

  for(Int i=0;i<3;i++)
    if(vs[i+1]!=vs[i]+1) drop("No");
  drop("Yes");
  return 0;
}