#include <bits/stdc++.h>

using namespace std;

int main()
{
  int n;
  cin>>n;
  string s;
  cin>>s;
    vector<char> s1;
    
  for(int i=n-1;i>=0;i--)
  {
      char t1=s[i];
      char t;
      auto it1=find(s1.begin(),s1.end(),t1);
    if(it1==s1.end()) {
        s1.push_back(t1);
        char t=s[i];
    }
    else if(t1>t){
        s1.push_back(t1);
        char t=t1;
    }
    
  }
  string ans;
  for(auto it=s1.begin();it!=s1.end();it++){
      ans+=*it;
  }
  cout<<ans<<endl;
    // string a="pranav";
    // if(a.find('a')==true) cout<<"yes"<<endl;
    // else cout<<"no"<<endl;
    return 0;
}