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

int main()
{
	int n[4];
	cin >> n[0] >> n[1] >> n[2] >> n[3];

	sort( n, n + 4 );
	string ans = "No";
	if( n[0] + 1 == n[1] &&
		n[1] + 1 == n[2] &&
		n[2] + 1 == n[3] ) ans = "Yes";

	cout << ans << endl;
}