use std::io;

#[derive(Clone, Copy)]
struct Card {
    number: [u64; 2],
}

struct Problem {
    cards: Vec<Card>,
    operation_count: usize,
}

fn read_problem() -> Problem {
    // 標準入力からの読み取り用バッファ
    let mut input = String::new();

    // N の読み取り
    io::stdin().read_line(&mut input).expect("Failed to read line");
    let n: usize = input.trim().parse().expect("Input was not a number");

    // 各 A_i, B_i の読み取り
    let mut pairs = Vec::new(); // (A_i, B_i) のペアを格納するベクター
    for _ in 0..n {
        input.clear(); // バッファをクリア
        io::stdin().read_line(&mut input).expect("Failed to read line");

        // 空白で分割し、それぞれ u64 として解析
        let parts: Vec<u64> = input
            .trim()
            .split_whitespace()
            .map(|x| x.parse().expect("Input was not a number"))
            .collect();

        if parts.len() != 2 {
            eprintln!("Invalid input format");
            continue;
        }

        // ベクターに追加
        pairs.push((parts[0], parts[1]));
    }

    let cards = pairs
        .into_iter()
        .map(|(v1, v2)| Card { number: [v1, v2] })
        .collect::<Vec<_>>();

    Problem {
        cards,
        operation_count: 50,
    }
}

#[derive(Clone)]
struct State {
    card_pool: Vec<Card>,
}

const TARGET_VALUE: u64 = 50_0000_0000_0000_0000;

impl State {
    fn new(problem: &Problem) -> State {
        State {
            card_pool: problem.cards.clone(),
        }
    }

    fn copy_from(&mut self, state: &State) {
        for i in 0..state.card_pool.len() {
            self.card_pool[i] = state.card_pool[i]
        }
    }

    fn manipulate(&mut self, c1: usize, c2: usize) {
        let first = (self.card_pool[c1].number[0] + self.card_pool[c2].number[0]) / 2;
        let second = (self.card_pool[c1].number[1] + self.card_pool[c2].number[1]) / 2;

        self.card_pool[c1].number[0] = first;
        self.card_pool[c2].number[0] = first;

        self.card_pool[c1].number[1] = second;
        self.card_pool[c2].number[1] = second;
    }
}

fn calculate_cost_diff(first: u64, second: u64) -> u64 {
    first.abs_diff(TARGET_VALUE).max(second.abs_diff(TARGET_VALUE))
}

fn simulate_with_greedy(problem: &Problem, state: &mut State, turn: usize) -> u64 {
    let mut state = state.clone();
    for _iter in 0..turn {
        // 平均化して改善率の最も高い組合せを選択
        let mut best_improve_pair = (0, 0);
        let mut best_gain = std::i64::MIN;
        let c1 = 0;
        for c2 in c1 + 1..state.card_pool.len() {
            let first = (state.card_pool[c1].number[0] + state.card_pool[c2].number[0]) / 2;
            let second = (state.card_pool[c1].number[1] + state.card_pool[c2].number[1]) / 2;

            let before_c1_diff = calculate_cost_diff(state.card_pool[c1].number[0], state.card_pool[c1].number[1]);
            let before_c2_diff = calculate_cost_diff(state.card_pool[c2].number[0], state.card_pool[c2].number[1]);
            let before_diff = before_c1_diff + before_c2_diff;

            let after_diff = calculate_cost_diff(first, second) * 2;
            let gain = before_diff as i64 - after_diff as i64;

            if best_gain < gain {
                best_gain = gain;
                best_improve_pair = (c1, c2);
            }
        }
        let (c1, c2) = best_improve_pair;
        state.manipulate(c1, c2);
    }
    // calculate score
    // ⌊2000000−100000 log 10 (max(V_1 ,V_2)+1)⌋
    let diff = calculate_cost_diff(state.card_pool[0].number[0], state.card_pool[0].number[1]);
    (200_0000f64 - 10_0000f64 * (diff as f64).log10()).floor() as u64
}

fn solve(problem: &Problem) -> Vec<(usize, usize)> {
    let mut state = State::new(problem);
    let mut init_state = State::new(problem);

    let mut ret = vec![];

    for turn in 1..=problem.operation_count {
        // 平均化して改善率の最も高い組合せを選択
        let mut best_improve_pair = (0, 0);
        let mut best_score = std::u64::MIN;
        let c1 = 0;
        for c2 in c1 + 1..state.card_pool.len() {
            init_state.copy_from(&state);
            init_state.manipulate(c1, c2);
            let score = simulate_with_greedy(problem, &mut init_state, problem.operation_count - turn);
            if best_score < score {
                best_score = score;
                best_improve_pair = (c1, c2);
            }
        }
        let (c1, c2) = best_improve_pair;
        state.manipulate(c1, c2);

        ret.push((c1 + 1, c2 + 1));
    }

    ret
}

fn main() {
    let problem = read_problem();

    let ret = solve(&problem);

    println!("{}", ret.len());
    for (c1, c2) in ret.iter() {
        println!("{} {}", c1, c2);
    }
}