#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
    
    ll v[4];
    cin >> v[0],v[1],v[2],v[3];
    vector<ll> vc (begin(v), end(v));
    sort(vc.begin(), vc.end());
    for(int i; i<vc.size() -1 ; i++){
        if(vc[i]+1 != vc[i+1]){
            cout << "No" << endl;
        }
    }
    cout << "Yes" << endl;
}