#include <iostream>
#include <string>
using namespace std;
int main()
{
string s;
cin>>s;
int times[26]={0};
for(int i=0;i<s.length();i++) times[s[i]-'a']+=1;
int index=0;
string result=s;
while(index<result.length())
{
if(result.substr(index)< result.substr(index+1) && times[result[index]-'a']>1 )
{
times[result[index]-'a']--;
result=result.substr(0,index)+result.substr(index+1);
index=0;
}
else index++;
}
cout<<result;
return 0;
}