use std::{collections::HashSet, io};

#[derive(Debug)]
pub struct Xorshift {
    seed: u64,
}
impl Xorshift {
    pub fn new() -> Xorshift {
        Xorshift {
            seed: 0xf0fb588ca2196dac,
        }
    }

    pub fn with_seed(seed: u64) -> Xorshift {
        Xorshift { seed }
    }

    pub fn next(&mut self) -> u64 {
        self.seed = self.seed ^ (self.seed << 13);
        self.seed = self.seed ^ (self.seed >> 7);
        self.seed = self.seed ^ (self.seed << 17);
        self.seed
    }

    pub fn next_u128(&mut self) -> u128 {
        let first = self.next() as u128;
        let second = self.next() as u128;
        (first << 64) + second
    }

    pub fn rand(&mut self, m: u64) -> u64 {
        self.next() % m
    }

    // 0.0 ~ 1.0
    pub fn randf(&mut self) -> f64 {
        use std::mem;
        const UPPER_MASK: u64 = 0x3FF0000000000000;
        const LOWER_MASK: u64 = 0xFFFFFFFFFFFFF;
        let tmp = UPPER_MASK | (self.next() & LOWER_MASK);
        let result: f64 = unsafe { mem::transmute(tmp) };
        result - 1.0
    }
}

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

struct Problem {
    cards: Vec<Card>,
    operation_count: usize,
    hash_table: Vec<Vec<u128>>,
}

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<_>>();

    let mut xorshift = Xorshift::new();

    // table[card_id][select_count]
    let mut hash_table = vec![vec![0u128; 51]; n];
    for y in 0..n {
        for x in 0..51 {
            hash_table[y][x] = xorshift.next_u128();
        }
    }

    Problem {
        cards,
        operation_count: 50,
        hash_table,
    }
}

#[derive(Clone)]
struct State {
    card_pool: Vec<Card>,
    select_count: Vec<u8>,
    hash: u128,
    operation_list: Vec<(u8, u8)>,
}

const TARGET_VALUE: u64 = 50_0000_0000_0000_0000;

impl State {
    fn new(problem: &Problem) -> State {
        let mut hash = 0u128;
        for i in 0..problem.cards.len() {
            hash ^= problem.hash_table[i][0];
        }

        State {
            card_pool: problem.cards.clone(),
            select_count: vec![0; problem.cards.len()],
            hash,
            operation_list: vec![],
        }
    }

    fn copy_from(&mut self, state: &State) {
        for i in 0..state.card_pool.len() {
            self.card_pool[i] = state.card_pool[i]
        }
        self.select_count.resize(state.select_count.len(), 0);
        self.select_count.copy_from_slice(&state.select_count);
        self.hash = state.hash;
        self.operation_list.resize(state.operation_list.len(), (0, 0));
        self.operation_list.copy_from_slice(&state.operation_list);
    }

    fn manipulate(&mut self, problem: &Problem, 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.hash ^= problem.hash_table[c1][self.select_count[c1] as usize];
        self.hash ^= problem.hash_table[c2][self.select_count[c2] as usize];

        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;

        self.select_count[c1] += 1;
        self.select_count[c2] += 1;
        self.hash ^= problem.hash_table[c1][self.select_count[c1] as usize];
        self.hash ^= problem.hash_table[c2][self.select_count[c2] as usize];
        self.operation_list.push((c1 as u8, c2 as u8));
    }
}

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(problem, c1, c2);
    }
    // calculate score
    // ⌊2000000−100000 log 10 (max(V_1 ,V_2)+1)⌋
    // higher is better
    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_buffer1 = vec![State::new(problem)];
    let mut state_buffer2 = vec![];
    let mut init_state = state_buffer1[0].clone();

    let beam_width = 100;
    let mut diff_list = vec![];
    let mut hash_set = HashSet::<u128>::new();
    let mut xorshift = Xorshift::new();

    for turn in 1..=problem.operation_count {
        diff_list.clear();
        let (before_buffer, mut after_buffer) = if turn % 2 == 1 {
            (state_buffer1, state_buffer2)
        } else {
            (state_buffer2, state_buffer1)
        };

        for (i, s) in before_buffer.iter().enumerate() {
            let c1 = 0;
            for c2 in c1 + 1..s.card_pool.len() {
                init_state.copy_from(&s);
                init_state.manipulate(problem, c1, c2);
                let hash = init_state.hash;
                let score = simulate_with_greedy(problem, &mut init_state, problem.operation_count - turn);
                let noise = xorshift.next() % 100;
                let score = score * 100 + noise;
                diff_list.push((score as i64, hash, i, c1, c2));
            }
        }
        diff_list.sort_by_key(|p| -p.0);

        hash_set.clear();
        let mut ti = 0;
        for (_s, hash, si, c1, c2) in diff_list.iter() {
            if hash_set.contains(hash) {
                continue;
            }
            hash_set.insert(*hash);

            if after_buffer.len() <= ti {
                let state = State::new(problem);
                after_buffer.push(state);
            }
            after_buffer[ti].copy_from(&before_buffer[*si as usize]);
            after_buffer[ti].manipulate(problem, *c1, *c2);

            if after_buffer.len() >= beam_width {
                break;
            }
            ti += 1;
        }

        (state_buffer1, state_buffer2) = if turn % 2 == 1 {
            (before_buffer, after_buffer)
        } else {
            (after_buffer, before_buffer)
        };
    }
    state_buffer1[0]
        .operation_list
        .iter()
        .map(|(c1, c2)| (1 + *c1 as usize, 1 + *c2 as usize))
        .collect::<Vec<_>>()
}

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

    let ret = solve(&problem);

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