#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() { 
  ios::sync_with_stdio(false); cin.tie(0);
  //a
  int a[4];
  cin >> a[0] >> a[1] >> a[2] >> a[3];
  sort(a, a + 4);
  for (int i = 0; i < 3; i++) if (a[i] + 1 != a[i + 1]) { 
    cout << "No\n";
    return 0;
  }
  cout << "Yes\n";
  return 0;
}