Catalan

#include <bits/stdc++.h>

char myStr[25],ch1,ch2;
int digit;
int countA=0, countB=0;

void think(int index){

    if(index==2*digit) std::cout<<myStr<<"\n";
    else{
        myStr[index] = ch1;
        countA++;

        if(countA <= digit) think(index+1);
        countA--;

        myStr[index] = ch2;
        countB++;
        if(countA >=countB) think(index+1);
        countB--;
    }

}

int main(){

    std::cin>>digit;
    std::cin>>ch1>>ch2;

    myStr[2*digit]=0;
    think(0);

    return 0;
}