// yukicoder No.998
#include <bits/stdc++.h>
using namespace std;

int main()
{
  vector<int> v(4);
  for(int i = 0; i < 4; ++i) cin >> v[i];

  sort(v.begin(), v.end());

  int flag = true;
  for(int i = 0; i < 3; ++i) {
    if(v[i+1] != v[i] + 1) {
      flag = false;
      break;
    }
    else continue;
  }

  if(flag) cout << "Yes" << "\n";
  else cout << "No" << "\n";

  return 0;
}