#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
	int A, B, C, D;
	cin >> A >> B >> C >> D;
	vector<int> X = {A, B, C, D};
	sort(X.begin(), X.end());
	bool ok = true;
	for (int i = 0; i < 3; i++){
		if (X[i + 1] != X[i] + 1){
			ok = false;
		}
	}
	if (ok){
		cout << "Yes" << endl;
	} else {
		cout << "No" << endl;
	}
}