#include <bits/stdc++.h>
#include <vector>
#include <iostream>
#include <map>
#include <string>
#include <cmath>
#include <algorithm>
#include <queue>
#include <math.h>
#include <ctype.h>
#include <numeric>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repe(i,x,n) for(int i=x; i<(n); ++i)
#define pie 3.1415926535897932384
#define INF 10010010000
#define _GLIBCXX_DEBUG
#define All(a) (a).begin(),(a).end()
#define rAll(a) (a).rbegin(),(a).rend()
#define pb push_back
#define mk make_pair
#define yes cout << "Yes" << endl;
#define no cout << "No" << endl;
#define decimal cout << fixed << setprecision(20);
#define nextP next_permutation
#define em emplace_back
using ll = long long;
using P = pair<int, int>;
const ll MOD = 1000000007;
const ll INF1 = 1e18;
const ll mod = 998244353;

int main() {

    int A,B,C,D;
    cin >> A >> B >> C >> D;
    vector<int> s = {A,B,C,D};
    sort(All(s));
    for(int i=0; i<3; i++) {
        if(s[i]+1 != s[i+1]) {
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
    return 0;

}