#include <iostream>
#include <algorithm>
using namespace std;

int main() {
  string ans = "Yes";
  int a, b, c, d;
  cin >> a >> b >> c >> d;

  int xs[] = {a, b, c, d};
  sort(xs, end(xs));

  for (int i = 0; i < 3; i ++) {
    if (xs[i] + 1 != xs[i + 1]) {
      ans = "No";
      break;
    }
  }

  cout << ans << endl;
  return 0;
}