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

#define int long long

signed main(){
	int a[4];
	cin >> a[0] >> a[1] >> a[2] >> a[3];
	sort(a, a+4);

	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;
}