#include <bits/stdc++.h>

using namespace std;

int main() {
	int a, b, c, d;
	cin >> a >> b >> c >> d;

	int x[] = {a, b, c, d};
	sort(x, x+4);

	bool ok = true;
	for (int i = 0; i < 3; i++) {
		if (x[i]+1 != x[i+1]) {
			ok = false;
		}
	}

	if (ok) {
		puts("Yes");
	} else {
		puts("No");
	}

	return 0;
}