o62_mar_c1_socks

/// Interactive
#include "sockslib.h"
#include <bits/stdc++.h>
using namespace std;

const int inf = 1e9;
const int N = 2e3 + 10;
bool in[N];
int k, n;

bool Check(int s, int e, int cnt = 0){
    vector <int> socks;
    for(int i=s;i<=e;i++){
        if(in[i])
            socks.push_back(i), cnt ++;
    }
    return ask(socks) < cnt;
}

int main() {
    n = 2 * num();
    for(int i=1;i<=2*n;i++) in[i] = true;

    for(int i=1;i<=n;i++){
        int l = 1, r = i, mx = -inf;
        while(l <= r){
            int mid = (l + r) / 2;
            if(Check(mid, i))
                l = mid + 1, mx = max(mx, mid);
            else
                r = mid - 1;
        }
        if(mx != -inf){
            in[i] = in[mx] = false;
            match(i, mx);
        }
    }

    return 0;
}