#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll=long long;
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";
    }
    cout<<ans<<endl;
}