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

int main(void) {
	std::vector<int> num(4);
	
	for (int i = 0; i < 4; i++) {
		std::cin >> num.at(i);
	}

	std::sort(num.begin(), num.end());
	int a = 0;
	for (int j = 0; j < 3; j++) {
		if (num.at(j+1) - num.at(j) != 1) {
			a++;
		}
	}
		if (a == 0) {
			std::cout << "Yes" << std::endl;
		}
		else {
			std::cout << "No" << std::endl;
		}
	}