#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
template<class T> inline bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T&a,T b){if(a>b){a=b;return 1;}return 0;}
using ll = long long;

int a[4];

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

  rep(i,4) cin >> a[i];
  sort(a,a+4);
  cout << (a[0]+1==a[1] && a[1]+1==a[2] && a[2]+1==a[3] ? "Yes" : "No") << endl;
}