#include<bits/stdc++.h>
using namespace std;
int query(string str);
int query(string S, bool rv)
{
if (rv)
reverse(S.begin(), S.end());
return query(S);
}
void solve(int i, vector < bool > us, bool rv, string& cur, int N, int S)
{
if (cur.size() == N)
return;
for (int c = 0; c < S; c++)
if (us[c])
{
string tr = cur.substr(0, i);
tr += char('a'+c);
tr += cur.substr(i, cur.size()-i);
if (query(tr, rv) == tr.size())
{
cur = tr;
solve(i, us, rv, cur, N, S);
solve(i+1, us, rv, cur, N, S);
return;
}
else
us[c] = false;
}
}
string guess(int N, int S)
{
string cur = "";
vector < bool > us(S, true);
solve(0, us, false, cur, N, S);
reverse(cur.begin(), cur.end());
solve(cur.size(), us, true, cur, N, S);
reverse(cur.begin(), cur.end());
return cur;
}
