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

int main(){
    vector<int> N(4);
    for(auto &ni : N) cin >> ni;
    sort(N.begin(), N.end());
    if(N[0] + 1 == N[1]&&N[1] + 1 == N[2]&&N[2] + 1 == N[3]){
        cout << "Yes" << endl;
    }
    else cout << "No" << endl;
}