alternator letters

#include <bits/stdc++.h>
using namespace std;
///****************
string create() {
    string alfa = "";
    for (char c = 'a'; c <= 'z'; c++)
        alfa += c;
    return alfa;
}
const string alfa = create();
int n, k;
string st;

void bktr(int top) {
    if (n == top) {
        puts(st.c_str());
        return;
    }
    for (int i = 0; i < k; i++) {
        st[top] = alfa[i];
        bktr(top + 1);
    }
}

int main() {
    cin >> n >> k;
    assert(k >= 1 && k <= alfa.size());
    st.resize(n + 3);
    bktr(0);
    return 0;
}