#include <iostream>
#include <vector>
#include <algorithm>

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]) {
		if (A[1] + 1 == A[2]) {
			if (A[2] + 1 == A[3]) {
				cout << "Yes" << endl;
				return 0;
			}
		}
	}

	cout << "No" << endl;

	return 0;

}