#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

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