#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}
int main() {
	int a[4];
	for (auto &i : a) i = ri();
	std::sort(a, a + 4);
	bool res = true;
	for (int i = 0; i < 3; i++) if (a[i + 1] != a[i] + 1) res = false;
	puts(res ? "Yes" : "No");
	return 0;
}