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

typedef long long ll;
typedef pair<int, int> P;

#define mod 1000000007
#define inf 1000000000
#define all(x) (x).begin(), (x).end()
#define pb push_back

const long double PI = acos(-1);

ll gcd(ll a,ll b){return b ? gcd(b,a%b) : a;}
ll lcm(ll a,ll b){return a / gcd(a,b) * b;}

int main(){
  vector<ll> n(4);
  for(ll i = 0; i < 4; i++) cin >> n[i];
  sort(all(n));

  bool ok = true;
  for(ll i = 0; i < 3; i++){
    if(n[i]+1 != n[i+1]){
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  return 0;
}