#include<iostream>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
string s1,s2;
int main()
{
  for(int i=0;i<=18;i++)s1+=('a'+i);
  for(int i=0;i<106;i++)s2+=s1;
  while(s2.size()!=1)
  {
  	string s="";
  	for(int i=0;i<s2.size();i++)if((i+1)%2==0)s+=s2[i];
  	if(s.size()==1)
  	{
  	  cout<<s<<endl;
	  return 0;	
	}
	s2=s;
  }
  
}