#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

bool isFunc(vector<int> &v) {
  sort(v.begin(), v.end());
  rep(i, 0, 3) if (v[i + 1] - v[i] != 1) return false;
  return true;
}

void solve() {
  int N = 4;
  vector<int> v(N);
  rep(i, 0, N) { cin >> v[i]; }
  cout << ((isFunc(v)) ? "Yes" : "No") << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  getchar();
}