#include <bits/stdc++.h>
//#include <iostream>
#include <atcoder/all>
#include <math.h>
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rrep(i, n) for(int i = (n-1); i >= 0; i--)
using namespace std;
using namespace atcoder;
typedef long long ll;
const int MOD = 1000000007;
//const int MOD =  998244353;
 
const ll INF = 1LL<<61;
const int IINF = 1000000000;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

typedef pair<int, int> PI;
typedef pair<ll, ll> P;
typedef pair<string, ll> PS;

using mint = modint1000000007;


int main(){

    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    vector<int> ABCD(4);
    rep(i,4) cin >> ABCD[i];

    sort(ABCD.begin(), ABCD.end());
    bool isok = true;
    rep(i,3){
        if(ABCD[i] +1 != ABCD[i+1]){
            isok = false;
        }
    }
    if(isok) cout << "Yes" << endl;
    else cout << "No" << endl;
}