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

int main() {
	vector<int> a(4);
	for(int i=0; i<4; i++){
		cin >> a[i];
	}
	sort(a.begin(),a.end());
	if(a[0]+1==a[1] && a[1]+1==a[2] && a[2]+1==a[3]){
		cout << "Yes" << endl;
	}else{
		cout << "No" << endl;
	}
	return 0;
}