#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define TARGET 500000000000000000LL 
inline ll scoreCal(ll a0, ll a1, ll b0, ll b1) {
    ll newA = (a0 + a1) / 2;
    ll newB = (b0 + b1) / 2;
    ll score = max( abs(TARGET-newA), abs(TARGET-newB));
    return score;
}
inline ll scoreCal2(ll a0, ll b0) {
    return max(abs(TARGET-a0), abs(TARGET-b0));
}

int main() {
    // スタート時点のタイムスタンプ取得
    auto start_time = std::chrono::high_resolution_clock::now();

    int N;
    cin >> N;
    vector<ll> A(N), B(N);
    for (int i=0; i<N; ++i) {
        cin >> A[i] >> B[i];
    }
    vector<ll> Aorg, Borg;
    Aorg = A;
    Borg = B;

#if 1
    // 基準スコア作成(1固定で他のカードとペアリング)
    vector<pair<int, int>> ret;
    for (int i=0; i<50; ++i) {
        int u = 0;
        int v = 0;
        ll minScore = scoreCal2(A[0], B[0]);
        for (int j=1; j<N; ++j) {
            ll score = scoreCal(A[0], A[j], B[0], B[j]);
            if (score < minScore) {
                minScore = score;
                v = j;
            }
        }
        if (v == 0) {
            break;
        }
        ret.push_back(make_pair(u+1, v+1));
        ll newA = (A[u] + A[v]) / 2;
        ll newB = (B[u] + B[v]) / 2;
        A[u] = A[v] = newA;
        B[u] = B[v] = newB;
    }
    ll minScore = scoreCal2(A[0], B[0]);
    //cout << "minScore : " << minScore << endl;
#else
    ll minScore = TARGET;
#endif

    // 制限時間いっぱいまでランダムで計算
    //ll count = 0;
    //ll minA, minB;
    vector<pair<int, int>> ret1;
    int u;
    int v;
    // 終了時点のタイムスタンプ取得
    auto end_time = std::chrono::high_resolution_clock::now();
    // 経過時間の計算
    auto elapsed_time = std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count();
    srand(static_cast<unsigned>(time(NULL)));
    while(true) {
        //count++;
        A.clear();
        B.clear();
        ret1.clear();
        A = Aorg;
        B = Borg;
        for (int i=0; i<50; ++i) {
            u = rand()%N;
            v = rand()%N;
            while (u == v) {
                v = rand()%N;
            }
            ret1.push_back(make_pair(u+1, v+1));
            ll newA = (A[u] + A[v]) / 2;
            ll newB = (B[u] + B[v]) / 2;
            A[u] = A[v] = newA;
            B[u] = B[v] = newB;
        }
        ll tmpScore = scoreCal2(A[0], B[0]);
        if (tmpScore < minScore) {
            minScore = tmpScore;
            ret.clear();
            ret = ret1;
            //minA = A[0];
            //minB = B[0];
        }

        // 終了時点のタイムスタンプ取得
        end_time = std::chrono::high_resolution_clock::now();
        // 経過時間の計算
        elapsed_time = std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count();
        // 経過時間と制限時間の比較
        int time_limit = 970;  // 制限時間
        if (elapsed_time > time_limit) {
            break;
        }
    }
    //cout << "minScore : " << minScore << endl;
    //cout << count << endl;
    //cout << minA << " " << minB << endl;

    cout << ret.size() << endl;
    for (auto x : ret) {
        cout << x.first << " " << x.second << endl;
    }
    return 0;
}