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

int main() {
  int A[4];
  cin >> A[0] >> A[1] >> A[2] >> A[3];
  sort(A, A + 4);
  if (A[1] == A[0] + 1 && A[2] == A[1] + 1 && A[3] == A[2] + 1)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}