#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
int query(string abc);
string calc(int l, int r, int len) {
if (l == r) {
string cur;
for (int i = 0; i < len; ++i) {
cur += char('a' + l);
}
int x = query(cur);
cur = "";
for (int i = 0; i < x; ++i) {
cur += char('a' + l);
}
return cur;
}
int mid = (l + r) >> 1;
string x = calc(l, mid, len);
string y = calc(mid + 1, r, len);
string res = "";
int px = 0, py = 0;
while (px < (int)x.size() and py < (int)y.size()) {
string g = res + x[px];
for (int i = py; i < (int)y.size(); ++i) {
g += y[i];
}
int cur_g = query(g);
if (cur_g > (int)res.size() + (int)y.size() - py) {
res += x[px++];
} else {
res += y[py++];
}
}
while (px < (int)x.size()) {
res += x[px++];
}
while (py < (int)y.size()) {
res += y[py++];
}
return res;
}
string guess(int _N, int _C) {
return calc(0, _C - 1, _N);
}
