#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int>vi;
#define pb push_back
#define sz(x) (int)x.size()
#define all(x) begin(x),end(x)
typedef string str;
#define FOR(i,a,b) for(int i=a; i<b; i++)
#define ROF(i,a,b) for(int i=b-1; i>=a; i--)
void ckmin(int &x, int y){x=min(x,y);}
//------------------------------------
int query(string S);
int alp;
void upd(str &s, int idx, char c){
str ss;
FOR(i,0,sz(s)+1){
if(i==idx) ss+=c;
if(i<sz(s)) ss+=s[i];
}
s=ss;
}
bool check(str s, int idx, char c){
str ss;
FOR(i,0,idx) ss+=s[i];
ss+=c;
int x=sz(ss);
FOR(i,idx,sz(s)) if(s[i]==c) ss+=s[i];
return query(ss)==sz(ss);
}
str guess(int N, int S){
alp=S;
vi nb(alp);
for(char c='a'; c<=char('a'+alp-1); c++){
str s;
FOR(i,0,N) s+=c;
nb[c-'a']=query(s);
}
int idx=0;
FOR(i,0,alp) if(nb[i]>nb[idx]) idx=i;
str cur;
FOR(i,0,nb[idx]) cur+=char(idx+'a');
FOR(i,0,alp) if(i!=idx){
char c=i+'a';
while(nb[i]--){
int l=0,r=sz(cur),ind=-1;
while(l<=r){
int m=(l+r)/2;
if(check(cur,m,c)){
ind=m;
l=m+1;
}
else r=m-1;
}
upd(cur,ind,c);
}
}
//cout << sz(cur) << endl;
return cur;
}
