#include <bits/stdc++.h>
#define Int int64_t

using namespace std;

int main() {
	vector<int> v(4);
	for (int i = 0; i < 4; ++i) { cin >> v[i]; }

	sort(v.begin(), v.end());
	bool ok = true;
	for (int i = 0; i + 1 < 4; ++i) {
		if (v[i] + 1 != v[i + 1]) { ok = false; }
	}
	cout << (ok ? "Yes" : "No") << endl;

	return 0;
}