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

int main(){
	vector<int>v(4); for(auto&&i:v)cin>>i;
	sort(v.begin(),v.end());
	for(auto i=v.begin()+1;i!=v.end();++i){
		if(*i-*(i-1)!=1){
			cout<<"No\n"s;
			return 0;
		}
	}
	cout<<"Yes\n"s;
}