#include <vector>
#include <iostream>
#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());
	bool ok = true;
	for (int i = 0; i < 3; ++i) {
		if (A[i + 1] - A[i] != 1) ok = false;
	}
	cout << (ok ? "Yes" : "No") << endl;
	return 0;
}