#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <tuple>
#include <deque>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef pair<int, double> Pid;
typedef pair<double, int> Pdi;
typedef pair<ll, int> Pl;
typedef pair<int, pair<int, int>> PP;
const double PI = 3.1415926535897932;   // acos(-1)
const double EPS = 1e-15;
const int INF = 1001001001;
const int mod = 1e+9 + 7;

#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define chadd(x, y) x = (x + y) % mod

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    vector<int> a(4);
    for(int i = 0; i < 4; ++i)  cin >> a[i];
    sort(a.begin(), a.end());
    for(int i = 0; i < 3; ++i){
        if(a[i] + 1 != a[i+1]){
            cout << "No\n";
            return 0;
        }
    }
    cout << "Yes\n";
}