#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    vector<int> a(4);
    for (int i = 0; i < 4; ++i) {
        cin >> a[i];
    }

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

    cout << (a[0] + 1 == a[1] && a[1] + 1 == a[2] && a[2] + 1 == a[3] ? "Yes" : "No") << endl;
    return 0;
}