#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

namespace {

constexpr int K = 16;
constexpr int S = 1;

void solve() {
  int n;
  scan(n);
  std::vector<i64> a(n), b(n);
  for (const int i : rep(n)) {
    scan(a[i], b[i]);
    a[i] >>= S;
    b[i] >>= S;
  }

  std::vector<int> p(n);
  std::iota(p.begin(), p.end(), 0);
  i64 s = 0;
  i64 t = 0;
  for (const int i : rep(K)) {
    s += a[i];
    t += b[i];
  }

  const auto evaluate = [&] {
    constexpr i64 H = (500'000'000'000'000'000 >> S) * K;
    return std::max(std::abs(s - H), std::abs(t - H));
  };

  i64 cur = evaluate();
  i64 best = cur;
  auto ans = p;
  for (const auto& sa : Sa<256>(1 << 25, 1e20, 1e15)) {
    const int i = randint(1, K - 1);
    const int j = randint(K, n - 1);
    s += a[p[j]] - a[p[i]];
    t += b[p[j]] - b[p[i]];
    std::swap(p[i], p[j]);
    const i64 nxt = evaluate();
    if (cur + sa.tol < nxt) {
      std::swap(p[i], p[j]);
      s -= a[p[j]] - a[p[i]];
      t -= b[p[j]] - b[p[i]];
    } else {
      cur = nxt;
    }

    if (chmin(best, cur)) {
      ans = p;
    }
  }

  print(K - 1);
  for (int k = 1; k < K; k *= 2) {
    for (int i = 0; i < K; i += k * 2) {
      print(ans[i] + 1, ans[i + k] + 1);
    }
  }
}

}  // namespace

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout << std::setprecision(DBL_DECIMAL_DIG);

  solve();
}

#else  // __INCLUDE_LEVEL__

#include <bits/stdc++.h>

namespace xorshift {

using u64 = std::uint64_t;
using u128 = ::__uint128_t;

inline u64 x = std::chrono::steady_clock::now().time_since_epoch().count();

inline u64 next() {
  x ^= x << 7;
  x ^= x >> 9;
  return x;
}

int randint(int a, int b) {
  const u64 m = static_cast<u64>(b) - static_cast<u64>(a) + 1;
  return a + static_cast<int>(u128{next()} * m >> 64);
}

template <std::ranges::random_access_range R>
void shuffle(R&& r) {
  const int n = static_cast<int>(std::ranges::size(r));
  if (n < 2) {
    return;
  }
  for (const int i : std::views::iota(1, n)) {
    if (const int j = randint(0, i); j < i) {
      std::ranges::swap(r[i], r[j]);
    }
  }
}

double uniform() { return static_cast<double>(next()) / static_cast<double>(UINT64_MAX); }
double uniform(double a, double b) { return a + (b - a) * uniform(); }

}  // namespace xorshift

using xorshift::randint;
using xorshift::shuffle;
using xorshift::uniform;

template <int UpdateInterval = 1>
class Sa {
 public:
  explicit Sa(std::int64_t n_iters, double start_temp = 0, double end_temp = 0)
      : n_iters_(n_iters),
        start_temp_(start_temp),
        cooling_rate_(start_temp ? end_temp / start_temp : 1),
        iter_(0),
        elapsed_(0),
        temp_(start_temp) {
    assert(0 <= end_temp && end_temp <= start_temp);
  }

  Sa begin() const { return *this; }
  int end() const { return 0; }

  bool operator!=(int) const { return iter_ < n_iters_; }

  void operator++() {
    if (++iter_ % UpdateInterval == 0) {
      elapsed_ = static_cast<double>(iter_) / static_cast<double>(n_iters_);
      temp_ = start_temp_ * std::pow(cooling_rate_, elapsed_);
    }
  }

  auto operator*() const {
    struct {
      std::int64_t iter;
      double elapsed;
      double temp;
      double tol;
    } sa{iter_, elapsed_, temp_, temp_ * -std::log(uniform())};
    return sa;
  }

 private:
  std::int64_t n_iters_;
  double start_temp_;
  double cooling_rate_;
  std::int64_t iter_;
  double elapsed_;
  double temp_;
};

template <class T, class U = T>
bool chmin(T& x, U&& y) {
  return y < x && (x = std::forward<U>(y), true);
}

template <class T, class U = T>
bool chmax(T& x, U&& y) {
  return x < y && (x = std::forward<U>(y), true);
}

template <std::signed_integral T = int>
T inf() {
  T ret;
  std::memset(&ret, 0x3f, sizeof(ret));
  return ret;
}

template <std::floating_point T>
T inf() {
  return std::numeric_limits<T>::infinity();
}

template <class T>
concept Range = std::ranges::range<T> && !std::convertible_to<T, std::string_view>;

template <class T>
concept Tuple = std::__is_tuple_like<T>::value && !Range<T>;

namespace std {

istream& operator>>(istream& is, Range auto&& r) {
  for (auto&& e : r) {
    is >> e;
  }
  return is;
}

istream& operator>>(istream& is, Tuple auto&& t) {
  return apply([&](auto&... xs) -> istream& { return (is >> ... >> xs); }, t);
}

ostream& operator<<(ostream& os, Range auto&& r) {
  for (string_view sep = ""; auto&& e : r) {
    os << exchange(sep, " ") << e;
  }
  return os;
}

ostream& operator<<(ostream& os, Tuple auto&& t) {
  const auto f = [&](auto&... xs) -> ostream& {
    [[maybe_unused]] string_view sep = "";
    ((os << exchange(sep, " ") << xs), ...);
    return os;
  };
  return apply(f, t);
}

}  // namespace std

void scan(auto&&... xs) { std::cin >> std::tie(xs...); }
void print(auto&&... xs) { std::cout << std::tie(xs...) << '\n'; }

template <class F>
class fix {
 public:
  explicit fix(F f) : f_(std::move(f)) {}

  decltype(auto) operator()(auto&&... xs) const {
    return f_(std::ref(*this), std::forward<decltype(xs)>(xs)...);
  }

 private:
  F f_;
};

inline auto rep(int l, int r) { return std::views::iota(std::min(l, r), r); }
inline auto rep(int n) { return rep(0, n); }
inline auto rep1(int l, int r) { return rep(l, r + 1); }
inline auto rep1(int n) { return rep(1, n + 1); }

namespace ranges = std::ranges;
namespace views = std::views;

using i64 = std::int64_t;

#endif  // __INCLUDE_LEVEL__