#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <numeric>

using namespace std;
using ull = unsigned long long;
#define Mod %1000000007

int main() 
{
	std::vector<int> v(4);
	for (int i = 0; i < 4; i++)
		cin >> v[i];
	std::sort(v.begin(), v.end());

	bool f = true;
	for (int i = 0; i < 3; i++)
		if (v[i + 1] - v[i] != 1)
		{
			f = false;
			break;
		}

	if (f)
		cout << "Yes" << endl;
	else
		cout << "No" << endl;

	return 0;
}