#pragma GCC optimize("Ofast", "unroll-loops")

#include <bits/stdc++.h>

using namespace std;

int main() {
	vector<int> nums(4);
	for (int i = 0; i < 4; ++i)
		cin >> nums[i];
	sort(nums.begin(), nums.end());
	bool f = true;
	for (int i = 0; i < 4 - 1; ++i)
		f = f && (nums[i + 1] == nums[i] + 1);
	cout << (f ? "Yes" : "No") << endl;
	return 0;
}