#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

using Pair = pair<int, int>;
using Tuple = tuple<int, int, int>;
using VI1 = vector<int>;
using VI2 = vector<VI1>;
using VL1 = vector<ll>;
using VL2 = vector<VL1>;
using VD1 = vector<ld>;
using VD2 = vector<VD1>;
using VB1 = vector<bool>;
using VB2 = vector<VB1>;
using VP1 = vector<Pair>;
using VP2 = vector<VP1>;
using VT1 = vector<Tuple>;
using VT2 = vector<VT1>;

using Queue = queue<int>;
using DQ = deque<int>;
using PQ = priority_queue<int, vector<int>, greater<int>>;
using Table = VI2;
using Graph = VI2;

/** io */
template <typename T>
std::vector<T> input_vec(int N);
template <typename T>
void output_row(std::vector<T> &row);
template <typename T>
void output_col(std::vector<T> &col);
void outputYesNo(bool yes, const string &Yes = "Yes", const string &No = "No");
/** minmax */
template <typename T>
bool chmin(T &a, T b);
template <typename T>
bool chmax(T &a, T b);

template <typename T>
T calc_gcd(T a, T b) {
  if (b == 0) return a;
  return calc_gcd(b, a % b);
}

template <typename T>
T calc_lcm(T a, T b) {
  assert(a > 0 && b > 0);
  T gcd = calc_gcd(a, b);
  return a / gcd * b;
}

auto solve() {
  int N;
  cin >> N;
  VI1 x(N), y(N);
  for (int i = 0; i < N; ++i) {
    cin >> x.at(i) >> y.at(i);
  }
  VI1 I(N);
  iota(I.begin(), I.end(), 0);
  auto comp = [&x, &y](int a, int b) -> bool {
    auto xa = x.at(a), ya = y.at(a);
    auto xb = x.at(b), yb = y.at(b);
    return (xa * yb - ya * xb > 0);
  };
  sort(I.begin(), I.end(), comp);
  VP1 zw;
  for (int i = 0, j = 1; j < N; i += 2, j += 2) {
    zw.emplace_back(I.at(i) + 1, I.at(j) + 1);
  }
  return zw;
}

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  int t = 1;
  // cin >> t;
  while (t--) {
    auto result = solve();
    // cout << result << '\n';
    cout << result.size() << '\n';
    for (auto [zi, wi] : result) {
      cout << zi << ' ' << wi << '\n';
    }
    // output_row(result);
    // output_col(result);
    // outputYesNo(result, "Yes", "No");
  }
}

/** @note 使用頻度が高く毎回貼付するのが面倒なライブラリを実装しておく。*/

template <typename T>
std::vector<T> input_vec(int N) {
  std::vector<T> v(N);
  for (auto &vi : v) {
    cin >> vi;
  }
  return v;
}

void outputYesNo(bool yes, const string &Yes, const string &No) {
  if (yes)
    cout << Yes << '\n';
  else
    cout << No << '\n';
}

template <typename T>
void output_row(std::vector<T> &row) {
  int N = row.size();
  for (int i = 0; i < N; ++i) {
    if (i > 0) cout << ' ';
    cout << row.at(i);
  }
  cout << '\n';
}

template <typename T>
void output_col(std::vector<T> &col) {
  int N = col.size();
  for (int i = 0; i < N; ++i) {
    cout << col.at(i) << '\n';
  }
}

template <typename T>
bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T>
bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}