5. Zašifrovávať budeme vzorové riešenie

povodny_string = input()
pocet_vnoreni, kolkate_chcem = [int(i) for i in input().split()]
poctova_matica = [[0] * 26 for i in range(pocet_vnoreni)]
pismenk_matica = []
preskocene = 0
kolkate_pismenko = -1
possible = False

# vytvorenie si tabulky na co sa mi meni kazde pismeno
for i in range(26):
    pis = input()
    if pis == "#":
        pismenk_matica.append("")
    else:
        pismenk_matica.append(pis)
    # nahodenie to rovno aj do prveho riadku suctovej tabulky
    poctova_matica[0][i] = len(pismenk_matica[i])

# vytvorenie suctovej tabulky
for i in range(1, pocet_vnoreni):
    for j in range(26):
        poctova_matica[i][j] = sum(
            [poctova_matica[i - 1][ord(ch) - ord("a")] for ch in pismenk_matica[j]]
        )

# prejdenie cez prve slovo
i = -1
for j in range(len(povodny_string)):
    if (
        preskocene + poctova_matica[i][ord(povodny_string[j]) - ord("a")]
        < kolkate_chcem
        or pismenk_matica[ord(povodny_string[j]) - ord("a")] == ""
    ):
        preskocene += poctova_matica[i][ord(povodny_string[j]) - ord("a")]
    else:
        # ak sme nasli pismenko, ktore chceme tak nastavime, ze je to mozne a zapiseme si ktore pismenko to je
        possible = True
        kolkate_pismenko = ord(povodny_string[j]) - ord("a")
        break

if possible:
    # prejdenie az na poslednu vrstvu
    for i in range(pocet_vnoreni - 2, -1, -1):
        j = 0
        # dokym nenajdeme pismenko z ktoreho vznikne nase k-te pismenko
        while (
            preskocene
            + poctova_matica[i][ord(pismenk_matica[kolkate_pismenko][j]) - ord("a")]
            < kolkate_chcem
            or pismenk_matica[kolkate_pismenko] == ""
        ):
            preskocene += poctova_matica[i][
                ord(pismenk_matica[kolkate_pismenko][j]) - ord("a")
            ]
            j += 1
        # zapiseme si ktore pismenko to je
        kolkate_pismenko = ord(pismenk_matica[kolkate_pismenko][j]) - ord("a")

    # z poslednej vrstvy urcenie finalneho pismenka
    kolkate_pismenko = pismenk_matica[kolkate_pismenko][kolkate_chcem - preskocene - 1]

    print(kolkate_pismenko)

else:
    print("Neexistuje")

#include <iostream>
#include <vector>
#include <string>
using namespace std;

struct nefinalne_pismenko{
	long long kolko_este;
	char pismenko;
};

int main(){
	
	string slovo;
	cin >> slovo;
	
	long long n,k;
	cin >> n >> k;
	
	vector<string> rules(26);
	for(long long i = 0; i < 26; i++){
		cin >> rules[i];
		if(rules[i] == "#"){
			rules[i] = "";
		}
	}
	
	vector<vector<long long>> lengths(26);
	for(long long i = 0; i < 26; i++){
		lengths[i].push_back(1);
	}
	
	for(long long i = 1; i <= n; i++){
		for(long long j = 0; j < 26; j++){
			string change = rules[j];
			long long result = 0;
			for(long long k = 0; k < change.length(); k++){
				result += lengths[change[k]-'a'][i-1];
			}
			lengths[j].push_back(result);
		}
	}
	
	vector<nefinalne_pismenko> stack;
	for(long long i = slovo.length()-1; i >= 0; i--){
		nefinalne_pismenko nove;
		nove.pismenko = slovo[i];
		nove.kolko_este = n;
		stack.push_back(nove);
	}
	
	long long este_zjest = k-1;
	
	while(true){
		
		if(stack.empty()){
			cout << "Neexistuje" << endl;
			break;
		}
		
		nefinalne_pismenko dalsie = stack[stack.size()-1];
		long long velkost_dalsieho = lengths[dalsie.pismenko-'a'][dalsie.kolko_este];
		
		if(velkost_dalsieho <= este_zjest){
			stack.pop_back();
			este_zjest -= velkost_dalsieho;
		}else{
			if(dalsie.kolko_este == 0){
				cout << dalsie.pismenko << endl;
				break;
			}
			stack.pop_back();
			long long new_depth = dalsie.kolko_este-1;
			string replacing_string = rules[dalsie.pismenko-'a'];
			for(long long i = replacing_string.length()-1; i >= 0; i--){
				nefinalne_pismenko nahrada;
				nahrada.pismenko = replacing_string[i];
				nahrada.kolko_este = new_depth;
				stack.push_back(nahrada);
			}
		}
		
	}
	
}