#include <bits/stdc++.h>  // clang-format off
using namespace std;
using Int = long long;
#define REP2(i, n) for (Int i = 0, max_i = (n); i < max_i; i++)
#define REP3(i, a, b) for (Int i = (a), max_i = (b); i < max_i; i++)
#define OVERLOAD2(_1, _2, _3, name, ...) name
#define REP(...) OVERLOAD2(__VA_ARGS__, REP3, REP2)(__VA_ARGS__)
struct SetupIO { SetupIO() { cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(13); } } setup_io;
#ifndef _MY_DEBUG
#define dump(...)
#endif  // clang-format on

/**
 *    author:  knshnb
 *    created: Fri Feb 28 21:19:56 JST 2020
 **/

signed main() {
    vector<Int> a(4);
    REP(i, 4) cin >> a[i];
    sort(a.begin(), a.end());
    REP(i, 4) {
        if (a[i] != a[0] + i) {
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}