#include <iostream>
#include <algorithm>
using namespace std;

int a[4];

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