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

using namespace std;

int main() {
    vector<int> a(4);

    for(int i=0; i<4; i++){
        cin >> a.at(i);
    }

    sort(a.begin(), a.end());

    if(a.at(0)+1 == a.at(1) && a.at(1)+1 == a.at(2) && a.at(2)+1 == a.at(3)){
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
}