/**
 *  author:   TakeruOkuyama
 *  created:  2020-04-09 12:39:57
**/
#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main(){
    vector<int> I(4);
    rep(i, 4){
        cin >> I[i];
    }
    sort(I.begin(), I.end());
    /*rep(i, 4){
        cout << I[i] << endl;
    }*/
    rep(i, 3){
        if(I[i + 1] - I[i] != 1){
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
return 0;}

/**
**/