#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;
const ll MOD = 1e9 + 7;
ll mod(ll x, ll m = MOD){return (x + m) % m;}
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<ll,ll> pll;
typedef vector<pair<int,int>> vpi;
#define pb push_back
#define ff first
#define ss second
#define all(x) (x).begin(),(x).end()
int n, s, k = 1;
int occ[64], rem[64];
string cur = "";
int query(string str);
string guess(int n, int s);
/*
string STR;
int query(string t)
{
int cur = 0;
for(int i =0; i < n; i++)
{
if(t[cur] == STR[i])
cur++;
}
return cur;
}
*/
int compare(int a, int b)
{
if(rem[a] <= 0)
return b;
if(rem[b] <= 0)
return a;
string t= cur;
t += (char) ('a' + a);
for(int u = 0; u < rem[b]; u++)
t += (char)('a' + b);
//cout << (char)('a' + a) << ' ' << (char)('a' +b) << ' ' << rem[a] << ' ' << rem[b] << '\n';
if(query(t) == (int)(t.length()))
return a;
else
return b;
}
vi st;
void build(int p, int l, int r)
{
if(l == r)
{
st[p] = l;
return ;
}
build(2 * p, l, (l + r)/2);
build(2 * p + 1, (l + r)/2 + 1, r);
st[p] = compare(st[2 * p], st[2 * p + 1]);
return ;
}
void update(int i)
{
i += k;
i /= 2;
while(i)
{
st[i] = compare(st[2 * i], st[2 * i + 1]);
i /= 2;
}
}
string guess(int N, int S)
{
n = N, s = S;
while(k < s)
k = (k << 1);
st.assign(2 * k + 1, 0);
for(int l = 0; l < s; l++)
{
string t= "";
for(int i = 0; i < N; i++)
t += (char)('a' + l);
occ[l] = query(t);
rem[l] = occ[l];
if(occ[l] == N)
return t;
}
build(1, 0, k - 1);
for(int i = 0; i < N; i++)
{
cur += (char)('a' + st[1]);
rem[st[1]]--;
update(st[1]);
}
return cur;
}
/*
int32_t main()
{
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int N, S;
cin >> N >> S;
cin >> STR;
cout << guess(N, S);
}
*/
