//*
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
//*/

#include <bits/stdc++.h>

// #include <atcoder/all>
// #include <atcoder/lazysegtree>

using namespace std;
// using namespace atcoder;

// #define _GLIBCXX_DEBUG

#define DEBUG(x) cerr << #x << ": " << x << endl;
#define DEBUG_VEC(v)                                        \
    cerr << #v << ":";                                      \
    for (int iiiiiiii = 0; iiiiiiii < v.size(); iiiiiiii++) \
        cerr << " " << v[iiiiiiii];                         \
    cerr << endl;
#define DEBUG_MAT(v)                                \
    cerr << #v << endl;                             \
    for (int iv = 0; iv < v.size(); iv++) {         \
        for (int jv = 0; jv < v[iv].size(); jv++) { \
            cerr << v[iv][jv] << " ";               \
        }                                           \
        cerr << endl;                               \
    }
typedef long long ll;
// #define int ll

#define vi vector<int>
#define vl vector<ll>
#define vii vector<vector<int>>
#define vll vector<vector<ll>>
#define vs vector<string>
#define pii pair<int, int>
#define pis pair<int, string>
#define psi pair<string, int>
#define pll pair<ll, ll>
template <class S, class T>
pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) {
    return pair<S, T>(s.first + t.first, s.second + t.second);
}
template <class S, class T>
pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template <class S, class T>
ostream &operator<<(ostream &os, pair<S, T> p) {
    os << "(" << p.first << ", " << p.second << ")";
    return os;
}
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define rrep(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rrep1(i, n) for (int i = (int)(n); i > 0; i--)
#define REP(i, a, b) for (int i = a; i < b; i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(), c.end()
void YES(bool t = true) {
    cout << (t ? "YES" : "NO") << endl;
}
void Yes(bool t = true) { cout << (t ? "Yes" : "No") << endl; }
void yes(bool t = true) { cout << (t ? "yes" : "no") << endl; }
void NO(bool t = true) { cout << (t ? "NO" : "YES") << endl; }
void No(bool t = true) { cout << (t ? "No" : "Yes") << endl; }
void no(bool t = true) { cout << (t ? "no" : "yes") << endl; }
template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const long double pi = 3.1415926535897932384626433832795028841971L;
int popcount(ll t) { return __builtin_popcountll(t); }
// int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
// int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
vi dx = {0, 0, -1, 1}, dy = {-1, 1, 0, 0};
vi dx2 = {1, 1, 0, -1, -1, -1, 0, 1}, dy2 = {0, 1, 1, 1, 0, -1, -1, -1};
struct Setup_io {
    Setup_io() {
        ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
        cout << fixed << setprecision(25);
        cerr << fixed << setprecision(25);
    }
} setup_io;
// const ll MOD = 1000000007;
const ll MOD = 998244353;
// #define mp make_pair
// #define endl '\n'

auto start = chrono::system_clock::now();
constexpr double TL = 0.98;

double calc_seconds() {
    return static_cast<double>(chrono::duration_cast<chrono::microseconds>(chrono::system_clock::now() - start).count() / 1000000.0);
}

class HRandom {
  public:
    HRandom() {
        random_mw = 1985;
        random_mz = 2012;
    }
    int intRandom() {
        random_mz = 36969 * (random_mz & 65535) + (random_mz >> 16);
        random_mw = 18000 * (random_mw & 65535) + (random_mw >> 16);
        unsigned result = (random_mz << 16) + random_mw;
        return result >> 1;
    }
    unsigned int uintRandom_65535() {
        // random_mz = 36969 * (random_mz & 65535) + (random_mz >> 16);
        // random_mw = 18000 * (random_mw & 65535) + (random_mw >> 16);
        // return random_mw & 65535;
        const unsigned tmp = random_mw & 65535;
        random_mw = 18000 * tmp + (random_mw >> 16);
        return tmp;
    }
    unsigned int uintRandom() {
        random_mz = 36969 * (random_mz & 65535) + (random_mz >> 16);
        random_mw = 18000 * (random_mw & 65535) + (random_mw >> 16);
        unsigned result = (random_mz << 16) + random_mw;
        return result;
    }
    double dblRandom() {
        random_mz = 36969 * (random_mz & 65535) + (random_mz >> 16);
        random_mw = 18000 * (random_mw & 65535) + (random_mw >> 16);
        unsigned result = (random_mz << 16) + random_mw;
        return (result + 1.0) * 2.328306435454494e-10;
    }

  private:
    unsigned random_mw;
    unsigned random_mz;
};

HRandom hrandom;

static uint32_t randxor() {
    static uint32_t x = 123456789;
    static uint32_t y = 362436069;
    static uint32_t z = 521288629;
    static uint32_t w = 88675123;
    uint32_t t;
    t = x ^ (x << 11);
    x = y;
    y = z;
    z = w;
    return w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
}
void randxor_init() {}

double randdouble() {
    return hrandom.dblRandom();
}
bool randbool(const float &p = 0.5) {
    return hrandom.uintRandom_65535() < (p * 65535);
}

inline int rnd(const int n) {
    assert(0 <= n);

    if (n == 1) {
        return 0;
    }
    return ((hrandom.uintRandom_65535()) * n) >> 16;
}

int rnd(const int &l, const int &r) {
    assert(l <= r);
    return rnd(r - l) + l;
}

class Parameter {
  public:
    double start_temp, end_temp;
    int hash_interval;
    int back_to_best_interval;
    int kick_interval;

    Parameter(double start_temp_ = 1.3042229737028601, double end_temp_ = 1e-06, int hash_interval_ = 82, int back_to_best_interval_ = 8335, int kick_interval_ = 2719266) {
        this->start_temp = start_temp;
        this->end_temp = end_temp;
        this->hash_interval = hash_interval;
        this->back_to_best_interval = back_to_best_interval;
        this->kick_interval = kick_interval;
    }

    static Parameter from_args(int argc, char **argv) {
        return Parameter(
            stof(argv[1]),
            stof(argv[2]),
            stoi(argv[3]),
            stoi(argv[4]),
            stoi(argv[5]));
    }
};

Parameter param;
std::default_random_engine engine(42);

constexpr int N = 45;
vector<pll> ab(N);

void input() {
    int x;
    cin >> x;
    rep(i, N) {
        cin >> ab[i].first >> ab[i].second;
    }
}

double calc_score(const vector<pii> &x) {
    auto now = ab;
    for (auto [u, v] : x) {
        pll s = now[u] + now[v];
        s.first /= 2;
        s.second /= 2;
        now[u] = now[v] = s;
    }
    return log10(max(abs(now[0].first - 5e17), abs(now[0].second - 5e17)) + 1);
}

pll calc_last(const vector<pii> &x) {
    auto now = ab;
    for (auto [u, v] : x) {
        pll s = now[u] + now[v];
        s.first /= 2;
        s.second /= 2;
        now[u] = now[v] = s;
    }
    return now[0];
}

signed main(int argc, char **argv) {
#ifdef LOCAL
    if (argc > 1) {
        param = Parameter::from_args(argc, argv);
    }
#endif
    input();

    constexpr int M = 50;
    vector<pii> x(M);
    int off = M - (N - 1);
    rep(i, off) {
        x[i] = {2 * i + 1, 2 * i + 2};
    }
    rep(i, N - 1) {
        x[off + i] = {0, i + 1};
    }
    double score = calc_score(x);

    constexpr int HASH_MAX = 65536;
    vector<pll> base_hash(M);
    vector<ll> value_hash(N);
    rep(i, M) {
        base_hash[i].first = hrandom.uintRandom_65535();
        base_hash[i].second = hrandom.uintRandom_65535();
    }
    rep(i, N) {
        value_hash[i] = hrandom.uintRandom_65535();
    }

    auto calc_hash = [&](const int &i) {
        // 現状の x で i のハッシュ値を計算
        ll ret = 0;
        ret ^= base_hash[i].first * value_hash[x[i].first];
        ret ^= base_hash[i].second * value_hash[x[i].second];
        return ret % HASH_MAX;
    };
    int current_hash = 0;
    rep(i, M) {
        current_hash ^= calc_hash(i);
    }

    vector<int> last_hash(HASH_MAX, -inf);

    double best_score = score;
    int best_hash = current_hash;
    vector<pii> best_x = x;
    double temperature = param.start_temp;
    int acc_rate1 = 0, acc_rate2 = 0;

    int last_best_update = 0, last_kick = 0;

    auto update_best = [&](int try_num, const double &new_score, const int &new_hash, const vector<pii> &new_x) {
        best_score = new_score;
        best_hash = new_hash;
        best_x = new_x;
        last_best_update = try_num;
        last_kick = try_num;
    };

    rep(try_num, inf) {
        if (try_num % (1 << 15) == 0) {
            // DEBUG((double)acc_rate / (1 << 15));
            // DEBUG(make_pair((double)acc_rate1 / (1 << 15), (double)acc_rate2 / (1 << 15)));
            acc_rate1 = acc_rate2 = 0;
        }

        if (try_num % 16 == 0) {
            double sec = calc_seconds();
            double rate = sec / TL;
            if (rate > 1) {
                DEBUG(try_num);
                break;
            }
            temperature = param.start_temp * (1 - rate) + param.end_temp * rate;
        }

        if (try_num - last_best_update > param.back_to_best_interval) {
            DEBUG("update");
            current_hash = best_hash;
            x = best_x;
            score = best_score;
            last_best_update = try_num;
        }

        if (try_num - last_kick > param.kick_interval) {
            DEBUG("kick");
            while (true) {
                int b = rnd(5, 10);
                int i1 = rnd(M - b), i2 = rnd(M - b);
                if (i1 > i2) {
                    swap(i1, i2);
                }
                if (i1 + b > i2) {
                    continue;
                }

                rep(i, b) {
                    current_hash ^= calc_hash(i1 + i) ^ calc_hash(i2 + i);
                    swap(x[i1 + i], x[i2 + i]);
                    current_hash ^= calc_hash(i1 + i) ^ calc_hash(i2 + i);
                }
                score = calc_score(x);
                break;
            }
            last_kick = try_num;
        }

        int op_type = rnd(11);
        int new_hash = current_hash;
        if (op_type < 9) {
            int idx1 = rnd(off, M - 1);
            int idx2 = rnd(off, min(idx1 + 5, M));
            new_hash ^= calc_hash(idx1) ^ calc_hash(idx2);
            swap(x[idx1], x[idx2]);
            new_hash ^= calc_hash(idx1) ^ calc_hash(idx2);

            if (last_hash[new_hash] > try_num - param.hash_interval) {
                swap(x[idx1], x[idx2]);
                continue;
            }

            double new_score = calc_score(x);
            double diff = score - new_score;
            double prob = exp(diff / temperature);
            if (randdouble() < prob) {
                acc_rate1++;
                score = new_score;
                current_hash = new_hash;
                last_hash[current_hash] = try_num;
                if (chmin(best_score, score)) {
                    update_best(try_num, score, current_hash, x);
                }
            } else {
                swap(x[idx1], x[idx2]);
            }
        } else if (op_type < 10) {
            int idx = rnd(off, M - 3);
            rep(i, 6) {
                if (i % 2 == 0) {
                    current_hash ^= calc_hash(idx) ^ calc_hash(idx + 1);
                    swap(x[idx], x[idx + 1]);
                    current_hash ^= calc_hash(idx) ^ calc_hash(idx + 1);
                } else {
                    current_hash ^= calc_hash(idx + 1) ^ calc_hash(idx + 2);
                    swap(x[idx + 1], x[idx + 2]);
                    current_hash ^= calc_hash(idx + 1) ^ calc_hash(idx + 2);
                }
                if (i == 5) {
                    break;
                }
                if (last_hash[current_hash] > try_num - param.hash_interval) {
                    continue;
                }

                double new_score = calc_score(x);
                double diff = score - new_score;
                double prob = exp(diff / temperature);
                if (randdouble() < prob) {
                    acc_rate1++;
                    score = new_score;
                    last_hash[current_hash] = try_num;
                    if (chmin(best_score, score)) {
                        update_best(try_num, score, current_hash, x);
                    }
                    break;
                }
            }
        } else {
            int idx = rnd(off);
            int b = rnd(2);
            int to = rnd(N);
            int ori;
            new_hash ^= calc_hash(idx);
            if (b) {
                if (x[idx].second == to) {
                    continue;
                }
                ori = x[idx].first;
                x[idx].first = to;
            } else {
                if (x[idx].first == to) {
                    continue;
                }
                ori = x[idx].second;
                x[idx].second = to;
            }
            new_hash ^= calc_hash(idx);
            if (last_hash[new_hash] > try_num - param.hash_interval) {
                if (b) {
                    x[idx].first = ori;
                } else {
                    x[idx].second = ori;
                }
                continue;
            }

            double new_score = calc_score(x);
            double diff = score - new_score;
            double prob = exp(diff / temperature);
            if (randdouble() < prob) {
                acc_rate2++;
                score = new_score;
                current_hash = new_hash;
                last_hash[current_hash] = try_num;
                if (chmin(best_score, score)) {
                    update_best(try_num, score, current_hash, x);
                }
            } else {
                if (b) {
                    x[idx].first = ori;
                } else {
                    x[idx].second = ori;
                }
            }
        }
    }

    ll val_hash = 0;
    rep(i, M) {
        val_hash ^= calc_hash(i);
    }
    assert(val_hash == current_hash);

    DEBUG(calc_last(best_x));
    DEBUG(best_score);
    int last_score = 2000000 - 100000 * best_score;
    DEBUG(last_score);

    cout << M << endl;
    for (auto [u, v] : best_x) {
        cout << u + 1 << " " << v + 1 << endl;
    }
}