#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

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