#include <bits/stdc++.h>
using namespace std;
using lint     = long long;
const lint inf = 1LL << 60;
const lint mod = 1000000007;

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());
    for (int i = 1; i < 4; ++i) {
        if (a[i] != a[i - 1] + 1) {
            cout << "No"
                 << "\n";
            return 0;
        }
    }
    cout << "Yes"
         << "\n";
    return 0;
}