#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>
using namespace std;
typedef long long LL;
typedef complex<double> CMP;

class STable { public:
	string getString(string s, string t, long long pos) 
	{
		const int S = s.size();
		const int T = t.size();
		vector< vector<LL> > len(S+1, vector<LL>(T+1));
		for(int i=1; i<=S; ++i)
			len[i][0] = 1;
		for(int k=1; k<=T; ++k)
			len[0][k] = 1;
		for(int i=1; i<=S; ++i)
		for(int k=1; k<=T; ++k)
			len[i][k] = len[i-1][k] + len[i][k-1];

		string ans;
		for(LL p=pos; p<min(pos+50, len[S][T]); ++p)
			ans += theChar(s, t, len, p, S, T);
		return ans;
	}

	char theChar(const string& s, const string & t, const vector< vector<LL> >& len, LL p, int i, int k)
	{
		if(i==0)
			return t[k-1];
		if(k==0)
			return s[i-1];

		if( early(s, t, i-1, k, i, k-1) )
			if( p < len[i-1][k] )
				return theChar(s,t,len,p,i-1,k);
			else
				return theChar(s,t,len,p-len[i-1][k],i,k-1);
		else
			if( p < len[i][k-1] )
				return theChar(s,t,len,p,i,k-1);
			else
				return theChar(s,t,len,p-len[i][k-1],i-1,k);
	}

	bool early(const string& s, const string & t, int i, int k, int ii, int kk)
	{
		string le,ri;
		for(int x=0; x<i; ++x) le += s[x];
		for(int x=0; x<k; ++x) le += t[x];
		for(int x=0; x<ii; ++x) ri += s[x];
		for(int x=0; x<kk; ++x) ri += t[x];
		sort(le.begin(), le.end());
		sort(ri.begin(), ri.end());
		return le <= ri;
	}
};

// 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(_, STable().getString(s, t, pos));}
int main(){

CASE(0)
	string s = "ad"; 
	string t = "cb"; 
	long long pos = 0LL; 
	string _ = "acbacd"; 
END
CASE(1)
	string s = "fox"; 
	string t = "cat"; 
	long long pos = 0LL; 
	string _ = "acfcfoacftacfcfocfox"; 
END
CASE(2)
	string s = "Ra6b1t"; 
	string t = "W0lf"; 
	long long pos = 66LL; 
	string _ = "RWab0RWRWa0RWl0RWRWa6RWa0RWRWa6RWa6RWab0RWRWa6RWa6"; 
END
CASE(3)
	string s = "M0HAXG"; 
	string t = "COFU12"; 
	long long pos = 919LL; 
	string _ = "MOFU2"; 
END
CASE(4)
	string s = "a0B1c2D3e4F5gHiJkLmN"; 
	string t = "A9b8C7d6EfGhIjKlMn"; 
	long long pos = 9876543210LL; 
	string _ = "B10AaB1c0Aa9Aa0AaB0AaB10AaB1c0AaB1c20Aa9Aa0AaB0Aa9"; 
END
CASE(5)
	string s = "TCOR2"; 
	string t = "MEDiUm"; 
	long long pos = 350LL; 
	string _ = "MTDEMTiCMTEMTDEMTDEMTiDEMTiUCMTEMTCMTOCMTEMTDEMTCM"; 
END
CASE(6)
	string s = "b"; 
	string t = "a"; 
	long long pos = 0LL; 
	string _ = "ab"; 
END
CASE(6)
	string s = "b"; 
	string t = "a"; 
	long long pos = 1LL; 
	string _ = "b"; 
END
CASE(7)
	string s = "01234abcdefghijklmnopqrstuvwxyz"; 
	string t = "56789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
	long long pos = 999999999LL; 
	string _ = "??"; 
END

}
// END CUT HERE
