#include<bits/stdc++.h>
using namespace std;
std::vector<int> ask(int i);
const int MAXN = 2e5;
int Ans = -1;
vector<int> A[MAXN];
int Max;
vector<int> ASK(int x) {
if(!A[x].size()) A[x] = ask(x);
if(A[x][0] + A[x][1] == 0) Ans = x;
return A[x];
}
int sumA(int x) {
ASK(x);
return A[x][0] + A[x][1];
}
void solve(int l, int r) {
if(l >= r || Ans != -1) return;
int mid = (l + r) / 2, ml = mid, mr = mid;
while(sumA(ml) < Max) ml--;
while(sumA(mr) < Max) mr++;
if(A[ml][0] - A[l][0] > 0) solve(l, ml);
if(A[r][0] - A[mr][0] > 0) solve(mr, r);
}
int find_best(int n) {
for(int i = 0; i < 500; i++) ask(0);
for(int i = 0; i < min(500, n); i++) {
Max = max(Max, sumA(i));
if(Max > 30) break;
}
int l = 0, r = n - 1;
while(sumA(l) < Max) l++;
while(sumA(r) < Max) r--;
solve(l, r);
return Ans;
}
