#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define endl "\n"
#define rep(i, a, n) for (int i = a; i < n; ++i)

int main() {
    vector<int> v(4);
    rep(i, 0, 4) cin >> v[i];

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

    rep(i, 0, 3) {
        if (v[i + 1] != v[i] + 1) {
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;

    return 0;
}