#include<bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<pl> vpl;
typedef vector<ld> vld;
typedef pair<ld, ld> pld;
typedef vector<pi> vpi;
//typedef tree<ll, null_type, less_equal<ll>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
template<typename T>
ostream &operator<<(ostream &os, vector<T> &a) {
os << "[";
for (int i = 0; i < ll(a.size()); i++) { os << a[i] << ((i != ll(a.size() - 1) ? " " : "")); }
os << "]\n";
return os;
}
#define all(x) x.begin(),x.end()
#define YES out("YES")
#define NO out("NO")
#define out(x){cout << x << "\n"; return;}
#define GLHF ios_base::sync_with_stdio(false); cin.tie(NULL);cout.tie(NULL)
#define print(x){for(auto ait:x) cout << ait << " "; cout << "\n";}
#define pb push_back
#define umap unordered_map
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
is >> p.first >> p.second;
return is;
}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> &p) {
os << "" << p.first << " " << p.second << "";
return os;
}
void usaco(string taskname) {
string fin = taskname + ".in";
string fout = taskname + ".out";
const char *FIN = fin.c_str();
const char *FOUT = fout.c_str();
freopen(FIN, "r", stdin);
freopen(FOUT, "w", stdout);
}
template<typename T>
void read(vector<T> &v) {
int n = v.size();
for (int i = 0; i < n; i++)
cin >> v[i];
}
template<typename T>
vector<T> UNQ(vector<T> a) {
vector<T> ans;
for (T t: a)
if (ans.empty() || t != ans.back())
ans.push_back(t);
return ans;
}
ll ceil(ll a, ll b) {
ll ans = a / b;
if (a % b)ans++;
return ans;
}
ld log(ld a, ld b) { return log(b) / log(a); }
ll power(ll base, ll exp, ll M = 1e18) {//(base^exp)%M
ll ans = 1;
while (exp) {
if (exp % 2 == 1)ans = ((ans % M) * (base % M)) % M;
base = ((base % M) * (base % M)) % M;
exp /= 2;
}
return ans;
}
string to_base(int n, int new_base) {
string s;
int nn = n;
while (nn) {
s += to_string(nn % new_base);
nn /= new_base;
}
reverse(all(s));
return s;
}
ll gcd(ll a, ll b) {
if (a < b)swap(a, b);
if (b == 0)return a;
return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
ll x = (a / gcd(a, b));
return b * x;
}
vl generate_array(ll n, ll mn = 1, ll mx = 1e18 + 1) {
if (mx == 1e18 + 1)
mx = n;
vl ans(n);
for (int i = 0; i < n; i++)
ans[i] = (mn + rand() % (mx - mn + 1));
return ans;
}
string substr(string s, int l, int r) {
string ans;
for (int i = l; i <= r; i++)
ans += s[i];
return ans;
}
int query(string);
vi cnt;
string merge(string s,string t){
for(int i=-1; i<int(s.size()); i++){
if(!t.size())break;
string cur=s.substr(0,i+1)+string(1,t[0])+s.substr(i+1,s.size()-(i+1));
if(query(cur)==cur.size()){
s=s.substr(0,i+1)+string(1,t[0])+s.substr(i+1,s.size()-(i+1));
t=t.substr(1,t.size()-1);
}
}
return s;
}
string dfs(int l,int r,int n){
if(l>r)return "";
else if(l==r)return string(cnt[l],l+'a');
int m=(l+r)/2;
return merge(dfs(l,m,n),dfs(m+1,r,n));
}
string guess(int n,int AB){
cnt=vi(26);
int sum=0;
for(int i=0; i<AB; i++){
int l=1,r=n-sum,ans=0;
while(l<=r){
int m=(l+r)/2;
if(query(string(m,('a'+i)))==m)
ans=m,l=m+1;
else
r=m-1;
}
cnt[i]=ans;
sum+=ans;
}
return dfs(0,AB-1,n);
}
