#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  vector<int> v(4);
  rep(i,4) cin >> v[i];
  sort(v.begin(), v.end());
  
  string ans = "Yes";
  if (v[0] != v[1]-1) ans = "No";
  if (v[1] != v[2]-1) ans = "No";
  if (v[2] != v[3]-1) ans = "No";
  cout << ans << endl;


}