#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int,int>;
#define rep(i,n) for(int i=0;i<n;i++)

const ll mod = ll(1e9) + 7;
const int INF = 1<<29;

int main(){
    vector<int> a(4);
    rep(i,4) cin >> a[i];
    sort(a.begin(),a.end());
    string ans = "Yes";
    rep(i,3){
        if (a[i]+1!=a[i+1]){
            ans = "No";
            break;
        }
    }
    cout << ans << endl;
    return 0;
}