#include <bits/stdc++.h>
#include <random>
using namespace std;
using ll = long long;
#define TARGET (500000000000000000)

random_device seed_gen;
mt19937 engine(seed_gen());
uniform_real_distribution<> uniform_distribution(0.0, 1.0);
double getRandomValue()
{
    return uniform_distribution(engine);
}

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

    vector<int> contribution(N, -1);
    contribution[0] = 0;
    for (int i = 1; i < N; i++)
    {
        int j = getRandomValue() * i;
        contribution[j]++;
        contribution[i] = contribution[j];
    }

    ll sumA = 0;
    ll sumB = 0;
    for (int i = 0; i < N; i++)
    {
        sumA += A[i] / (1LL << (contribution[i]));
        sumB += B[i] / (1LL << (contribution[i]));
    }

    clock_t start = clock();
    while (true)
    {
        clock_t end = clock();
        double elapsed = (double)(end - start) / CLOCKS_PER_SEC;
        if (elapsed > 0.90)
        {
            break;
        }

        ll score = max(abs(sumA - TARGET), abs(sumB - TARGET));
        if (false && getRandomValue() < 0.3)
        {
            // add
            vector<int> in, out;
            for (int i = 0; i < N; i++)
            {
                if (contribution[i] == -1)
                {
                    out.push_back(i);
                }
                else
                {
                    in.push_back(i);
                }
            }
            int i = getRandomValue() * out.size();
            i = out[i];
            int j = getRandomValue() * in.size();
            j = in[j];
            sumA -= A[j] / (1LL << contribution[j]);
            sumB -= B[j] / (1LL << contribution[j]);
            contribution[j]++;
            contribution[i] = contribution[j];
            sumA += A[j] / (1LL << contribution[j]);
            sumB += B[j] / (1LL << contribution[j]);
            sumA += A[i] / (1LL << contribution[i]);
            sumB += B[i] / (1LL << contribution[i]);

            ll score_tmp = max(abs(sumA - TARGET), abs(sumB - TARGET));
            if (score_tmp > score)
            {
                sumA -= A[j] / (1LL << contribution[j]);
                sumB -= B[j] / (1LL << contribution[j]);
                sumA -= A[i] / (1LL << contribution[i]);
                sumB -= B[i] / (1LL << contribution[i]);
                contribution[j]--;
                contribution[i] = 0;
                sumA += A[j] / (1LL << contribution[j]);
                sumB += B[j] / (1LL << contribution[j]);
            }
        }
        else if (false && getRandomValue() < 0.5)
        {
            // delete
            vector<int> in;
            for (int i = 1; i < N; i++)
            {
                if (contribution[i] != -1)
                {
                    in.push_back(i);
                }
            }
            if (in.size() == 0)
            {
                continue;
            }
            int i = getRandomValue() * in.size();
            i = in[i];
            vector<int> same;
            for (int j = 0; j < N; j++)
            {
                if (i == j)
                {
                    continue;
                }
                if (contribution[i] == contribution[j])
                {
                    same.push_back(j);
                }
            }
            if (same.size() == 0)
            {
                continue;
            }
        }
        else
        {
            int i = getRandomValue() * N;
            int j = getRandomValue() * N;
            if (contribution[i] == contribution[j])
            {
                continue;
            }
            sumA -= A[i] / (1LL << contribution[i]);
            sumB -= B[i] / (1LL << contribution[i]);
            sumA -= A[j] / (1LL << contribution[j]);
            sumB -= B[j] / (1LL << contribution[j]);
            swap(contribution[i], contribution[j]);
            sumA += A[i] / (1LL << contribution[i]);
            sumB += B[i] / (1LL << contribution[i]);
            sumA += A[j] / (1LL << contribution[j]);
            sumB += B[j] / (1LL << contribution[j]);

            ll score_tmp = max(abs(sumA - TARGET), abs(sumB - TARGET));
            if (score_tmp > score)
            {
                sumA -= A[i] / (1LL << contribution[i]);
                sumB -= B[i] / (1LL << contribution[i]);
                sumA -= A[j] / (1LL << contribution[j]);
                sumB -= B[j] / (1LL << contribution[j]);
                swap(contribution[i], contribution[j]);
                sumA += A[i] / (1LL << contribution[i]);
                sumB += B[i] / (1LL << contribution[i]);
                sumA += A[j] / (1LL << contribution[j]);
                sumB += B[j] / (1LL << contribution[j]);
            }
        }
    }

    vector<pair<int, int>> ans;
    priority_queue<pair<int, int>> pq;
    for (int i = 0; i < N; i++)
    {
        pq.push({contribution[i], i});
    }
    while (pq.size() > 1)
    {
        int u = pq.top().second;
        pq.pop();
        int v = pq.top().second;
        int d = pq.top().first;
        pq.pop();
        if (u > v)
        {
            swap(u, v);
        }
        ans.push_back({u, v});
        pq.push({d, u});
    }

    cout << ans.size() << '\n';
    for (auto [u, v] : ans)
    {
        cout << u + 1 << ' ' << v + 1 << '\n';
    }
}