#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(void) {
	vector<int> arr(4);
	for (int i = 0; i < 4; ++i) cin >> arr[i];
	sort(arr.begin(), arr.end());
	bool ok = true;
	for (int i = 1; i < 4; ++i) {
		if (arr[i - 1] + 1 != arr[i])
			ok = false;
	}
	cout << (ok ? "Yes" : "No") << endl;
	return 0;
}