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

int main() {
  int a[4];
  for (int i = 0; i < 4; i++) cin >> a[i];
  sort(a, a + 4);
  for (int i = 0; i < 3; i++) {
    if (a[i] + 1 != a[i + 1]) {
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  return 0;
}