#include <iostream>
#include <sstream>
#include <iomanip>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <iterator>
#include <functional>
#include <complex>
#include <queue>
#include <stack>
#include <cmath>
#include <cassert>
#include <cstring>
#ifdef __GNUC__
#include <ext/hash_map>
#define unordered_map __gnu_cxx::hash_map
#else
#include <unordered_map>
#endif
using namespace std;
typedef long long LL;
typedef complex<double> CMP;

class TheDictionary { public:
	string find(int n, int m, int k)
	{
		if( k <= C(n+m,n) )
			return rec(n, m, k);
		return "";
	}

	string rec(int n, int m, int k)
	{
		if( n+m == 0 )
			return "";
		if( n==0 )
			return "z" + rec(n, m-1, k);
		if( m==0 )
			return "a" + rec(n-1, m, k);

		LL c = C(n+m-1, m);
		if( k <= c )
			return "a" + rec(n-1, m, k);
		return "z" + rec(n, m-1, k - c);
	}

	LL C(int n, int k)
	{
		k = min(k, n-k);
		LL v = 1;
		for(int i=1; i<=k; ++i) {
			v = v * (n+1-i) / i;
			if( v >= (1LL<<50) )
				return v;
		}
		return v;
	}
};

// BEGIN CUT HERE
#include <ctime>
double start_time; string timer()
 { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
 { os << "{ ";
   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
void verify_case(const string& Expected, const string& Received) {
 bool ok = (Expected == Received);
 if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
 cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
#define END	 verify_case(_, TheDictionary().find(n, m, k));}
int main(){

CASE(0)
	int n = 2; 
	int m = 2; 
	int k = 2; 
	string _ = "azaz"; 
END
CASE(1)
	int n = 2; 
	int m = 2; 
	int k = 6; 
	string _ = "zzaa"; 
END
CASE(2)
	int n = 10; 
	int m = 10; 
	int k = 1000000000; 
	string _ = ""; 
END
CASE(3)
	int n = 7; 
	int m = 4; 
	int k = 47; 
	string _ = "aaazazaazaz"; 
END
/*
CASE(4)
	int n = ; 
	int m = ; 
	int k = ; 
	string _ = ; 
END
CASE(5)
	int n = ; 
	int m = ; 
	int k = ; 
	string _ = ; 
END
*/
}
// END CUT HERE
