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