#include <bits/stdc++.h>
#define rep(i,n) for(ll (i)=0;(i)<(n);(i)++)
#define repi(i,a,b) for(ll (i)=(a);(i)<(b);(i)++)
#define SIZE_OF_ARRAY(array)    (sizeof(array)/sizeof(array[0]))
typedef long long ll;
using namespace std;

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