#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <string>
#include <map>
#include <iterator>
#include <set>
#include <queue>
#include <bitset>

using namespace std;


int main() {

    int A, B, C, D;
    cin >> A >> B >> C >> D;
    vector<int> a = {A, B, C, D};
    sort(a.begin(), a.end());

    int t = a[0];
    bool ok = true;
    for (int i = 1; i < 4; ++i) {
        if (t + 1 != a[i]) {
            ok = false;
            break;
        } else {
            t = a[i];
        }
    }

    cout << (ok ? "Yes" : "No") << endl;
    return 0;
}