#include "bits/stdc++.h"
using namespace std;

int main() {
	long long A[4];
	cin >> A[0] >> A[1] >> A[2] >> A[3];
	sort(A, A + 4);
	if (A[0] + 1 == A[1] && A[1] + 1 == A[2] && A[2] + 1 == A[3]) cout << "Yes" << endl;
	else cout << "No" << endl;
}