#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
string ans, prov;
int cnt[N], nn, ss;
int query(string str);
string p, password;/*
int query(string q) {
int len = q.size();
int i = 0, j = 0, plen = password.size();
while (i < plen && j < len) {
while ((i < plen) && (password[i] != q[j])) {
i++;
}
if (i < plen) {
i++;
j++;
}
}
return j;
}*/
string join(string a, string b)
{
int na = a.size(), nb = b.size(), cur = nb;
string ans = "", aa = a, bb = b;
int la = 0, lb = 0;
while (la < na && lb < nb)
{
string mystr = ans + aa[0] + bb;
if (query(mystr) > cur)
{
cur++;
ans += aa[0];
aa.erase(aa.begin());
la++;
}
else
{
lb++;
ans += bb[0];
bb.erase(bb.begin());
}
}
ans += aa; ans += bb;
return ans;
}
string divide(int l, int r, int n)
{
string mystr = "";
if (l == r)
{
char a = l + 'a';
for (int i = 0; i < n; i++)
mystr += a;
int x = query(mystr);
mystr = "";
for (int i = 0; i < x; i++)
mystr += a;
return mystr;
}
int mid = (l + r) / 2;
return join(divide(l, mid, n), divide(mid + 1, r, n));
}
string guess(int n, int s)
{
return divide(0, s - 1, n);
}/*
int main()
{
freopen("x.in", "r", stdin);
freopen("x.out", "w", stdout);
int nn, ss;
cin >> nn >> ss;
cin >> password;
cout << guess(nn, ss);
return 0;
}*/
