#include "prize.h"
#include <bits/stdc++.h>
using namespace std;
int cnt;
int solve (int l, int r, int cl, int cr) {
if (l > r || cl + cr == cnt)
return 0;
if (l == r) {
vector<int> a = ask(l);
if (a[0] + a[1] == 0)
return l;
return 0;
}
int wef = cl + cr;
int mid = (l + r) >> 1;
int mn = mid, mx = mid;
bool L = true, R = true;
for (int i = 0; i < cnt - wef; i++) {
int x;
if (i % 2 == 1) {
x = mid + i / 2 + 1;
} else {
x = mid - i / 2;
}
mn = min (mn, x);
mx = max (mx, x);
vector<int> a = ask(x);
if (a[0] + a[1] == 0)
return x;
if (a[0] + a[1] == cnt) {
int ans = 0;
if (L) {
if (x == mn)
ans ^= solve (l, mn - 1, cl, a[1]);
else
ans ^= solve (l, mn - 1, cl, a[1] + i);
}
if (R) {
if (x == mx)
ans ^= solve (mx + 1, r, a[0], cr);
else
ans ^= solve (mx + 1, r, a[0] + i, cr);
}
return ans;
}
if (a[0] == 0)
L = false;
if (a[1] == 0)
R = false;
}
return 0;
}
int find_best(int n) {
for (int i = max (0, n - 473); i < n; i++) {
vector<int> a = ask(i);
if(a[0] + a[1] == 0)
return i;
cnt = max (cnt, a[0] + a[1]);
}
return solve (0, n - 1, 0, 0);
}
