#include <bits/stdc++.h>
#define rep(i,n)for(long long i=0;i<(n);i++)
using namespace std;
typedef long long ll;
const int MOD=1e9+7;
const int MAX = 510000;
const double pi=acos(-1);

int main(){
  vector<int>x(4);
  rep(i,4) cin >> x[i];
  sort(x.begin(),x.end());
  rep(i,3){
    if(x[i+1]!=x[i]+1){
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  return 0;
}