#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<ll, ll>;
#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
template<typename T> void chmin(T &a, const T &b) { a = min(a, b); }
template<typename T> void chmax(T &a, const T &b) { a = max(a, b); }
struct FastIO {FastIO() { cin.tie(0); ios::sync_with_stdio(0); }}fastiofastio;
#ifdef DEBUG_ 
#include "../program_contest_library/memo/dump.hpp"
#else
#define dump(...)
#endif
const ll INF = 1LL<<60;

int main(void) {
    vector<ll> v(4);
    REP(i, 4) cin >> v[i];
    sort(ALL(v));

    bool flag = true;
    FOR(i, 1, 4) {
        if(v[i] != v[i-1]+1) {
            flag = false;
        }
    }
    if(flag) cout << "Yes" << endl;
    else cout << "No" << endl;

    return 0;
}