#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 1'000'000'007; 

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	vector<int> a(4);
	
	
	for(int i = 0; i < 4; i++){
		cin>>a[i];
	}
	
	sort(a.begin(), a.end());
	
	for(int i = 1; i < 4; i++){
		if(a[i-1]+1 != a[i]) {
			cout<<"No"<<endl;
			return 0;
		}
	}
	
	cout<<"Yes"<<endl;
	
	return 0;
}