#include <bits/stdc++.h>
 using namespace std;
 using pii = pair<int, int>;
 using ll = long long;
 #define rep(i, j, n) for(int i = j; i < (int)(n); i++)
 const ll MOD = 1000000007;
 const ll INF = 1LL << 60;

int main() {
  vector<int> n(4);
  cin >> n.at(0) >> n.at(1) >> n.at(2) >> n.at(3);
  sort(n.begin(), n.end());
  bool ok = true;
  rep(i, 0, 3) {
    if (n.at(i) != n.at(i + 1) - 1) ok = false;
  }
  if (ok) cout << "Yes" << endl;
  else cout << "No" << endl;
}