#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  vector<int> x(4);
  REP (i, 4) cin >> x[i];
  sort(x.begin(), x.end());

  bool ck = true;
  REP (i, 3)
    ck &= x[i+1] - x[i] == 1;

  cout << (ck ? "Yes" : "No") << endl;
  
  return 0;
}