#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::cerr;
using std::endl;
using std::cin;

template<typename T>
std::vector<T> make_v(size_t a){return std::vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

int main() {
	std::vector<int> a(4);
	for(int i = 0; i < 4; i++) scanf("%d", &a[i]);
	sort(begin(a), end(a));

	for(int i = 0; i < 3; i++) {
		if(a[i] + 1 == a[i + 1]) continue;
		printf("No\n");
		return 0;
	}
	printf("Yes\n");
	return 0;
}