#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif

int main() {
    int64_t a, b, c, d;
    cin >> a >> b >> c >> d;

    vector<int64_t> xs = {a, b, c, d};
    ranges::sort(xs);

    bool flag = true;
    for (int64_t i = 0; i < 3; i++) {
        flag &= xs[i] + 1 == xs[i + 1];
    }

    cout << (flag ? "Yes" : "No") << endl;

    return 0;
}