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

int main() {
    const int n = 4;
    vector<int> a(n);
    for (auto &e : a) cin >> e;
    sort(a.begin(), a.end());
    
    bool ans = true;
    for (int i = 0; i+1 < n; i++) ans &= (a[i] + 1 == a[i+1]);
    cout << (ans ? "Yes" : "No") << endl;
    return 0;
}