#define _CRT_NONSTDC_NO_WARNINGS
#define _CRT_SECURE_NO_WARNINGS
#define ENABLE_DUMP
//#define ENABLE_PERF
#include <bits/stdc++.h>
#include <random>
#include <unordered_set>
#include <array>
#include <atcoder/all>
//#include <json.hpp>
//#include <boost/rational.hpp>
//#include <boost/multiprecision/cpp_int.hpp>
//using u128 = boost::multiprecision::uint128_t;
//using i128 = boost::multiprecision::int128_t;
#ifdef _MSC_VER
#include <conio.h>
#include <ppl.h>
#include <filesystem>
//#include <opencv2/core.hpp>
//#include <opencv2/highgui.hpp>
//#include <opencv2/imgproc.hpp>
#include <intrin.h>
int __builtin_clz(unsigned int n) { unsigned long index; _BitScanReverse(&index, n); return 31 - index; }
int __builtin_ctz(unsigned int n) { unsigned long index; _BitScanForward(&index, n); return index; }
namespace std { inline int __lg(int __n) { return sizeof(int) * 8 - 1 - __builtin_clz(__n); } }
#define __builtin_popcnt = __popcnt;
#define __builtin_popcntll = __popcnt64;
#else
#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#endif

/** compro_io **/
#ifdef ATCODER_MODINT_HPP
using mint = atcoder::modint998244353;
std::ostream& operator<<(std::ostream& os, const mint& m) {
    os << m.val();
    return os;
}
std::istream& operator>>(std::istream& is, mint& m) {
    uint64_t x;
    is >> x;
    m = x;
    return is;
}
#endif
namespace aux {
    template<typename T, unsigned N, unsigned L> struct tp { static void output(std::ostream& os, const T& v) { os << std::get<N>(v) << ", "; tp<T, N + 1, L>::output(os, v); } };
    template<typename T, unsigned N> struct tp<T, N, N> { static void output(std::ostream& os, const T& v) { os << std::get<N>(v); } };
}
template<typename... Ts> std::ostream& operator<<(std::ostream& os, const std::tuple<Ts...>& t) { os << '['; aux::tp<std::tuple<Ts...>, 0, sizeof...(Ts) - 1>::output(os, t); return os << ']'; } // tuple out
template<class Ch, class Tr, class Container> std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& os, const Container& x); // container out (fwd decl)
template<class S, class T> std::ostream& operator<<(std::ostream& os, const std::pair<S, T>& p) { return os << "[" << p.first << ", " << p.second << "]"; } // pair out
template<class S, class T> std::istream& operator>>(std::istream& is, std::pair<S, T>& p) { return is >> p.first >> p.second; } // pair in
std::ostream& operator<<(std::ostream& os, const std::vector<bool>::reference& v) { os << (v ? '1' : '0'); return os; } // bool (vector) out
std::ostream& operator<<(std::ostream& os, const std::vector<bool>& v) { bool f = true; os << "["; for (const auto& x : v) { os << (f ? "" : ", ") << x; f = false; } os << "]"; return os; } // vector<bool> out
template<class Ch, class Tr, class Container> std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& os, const Container& x) { bool f = true; os << "["; for (auto& y : x) { os << (f ? "" : ", ") << y; f = false; } return os << "]"; } // container out
template<class T, class = decltype(std::begin(std::declval<T&>())), class = typename std::enable_if<!std::is_same<T, std::string>::value>::type> std::istream& operator>>(std::istream& is, T& a) { for (auto& x : a) is >> x; return is; } // container in
template<typename T> auto operator<<(std::ostream& out, const T& t) -> decltype(out << t.stringify()) { out << t.stringify(); return out; } // struct (has stringify() func) out
/** io setup **/
struct IOSetup { IOSetup(bool f) { if (f) { std::cin.tie(nullptr); std::ios::sync_with_stdio(false); } std::cout << std::fixed << std::setprecision(15); } }
iosetup(true); // set false when solving interective problems
/** string formatter **/
template<typename... Ts> std::string format(const std::string& f, Ts... t) { size_t l = std::snprintf(nullptr, 0, f.c_str(), t...); std::vector<char> b(l + 1); std::snprintf(&b[0], l + 1, f.c_str(), t...); return std::string(&b[0], &b[0] + l); }
/** dump **/
#ifdef ENABLE_DUMP
#define DUMPOUT std::cerr
std::ostringstream DUMPBUF;
#define dump(...) do{DUMPBUF<<"  ";DUMPBUF<<#__VA_ARGS__<<" :[DUMP - "<<__LINE__<<":"<</*__PRETTY_FUNCTION__*/__FUNCTION__<<"]"<<std::endl;DUMPBUF<<"    ";dump_func(__VA_ARGS__);DUMPOUT<<DUMPBUF.str();DUMPBUF.str("");DUMPBUF.clear();}while(0);
void dump_func() { DUMPBUF << std::endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPBUF << head; if (sizeof...(Tail) == 0) { DUMPBUF << " "; } else { DUMPBUF << ", "; } dump_func(std::move(tail)...); }
#else
#define DUMP(...) void(0);
#endif
/* timer */
class Timer {
    double t = 0, paused = 0, tmp;
public:
    Timer() { reset(); }
    static double time() {
#ifdef _MSC_VER
        return __rdtsc() / 2.3e9;
#else
        unsigned long long a, d;
        __asm__ volatile("rdtsc"
            : "=a"(a), "=d"(d));
        return (d << 32 | a) / 2.3e9;
#endif
    }
    void reset() { t = time(); }
    void pause() { tmp = time(); }
    void restart() { paused += time() - tmp; }
    double elapsed_ms() const { return (time() - t - paused) * 1000.0; }
} timer;
/** perf counter **/
#if !defined(__PRETTY_FUNCTION__) && !defined(__GNUC__)
#define __PRETTY_FUNCTION__ __FUNCSIG__
#endif
struct PerfCounter {
    std::string name;
    Timer timer;
    PerfCounter(const std::string& name_) : name(name_) {}
    ~PerfCounter() {
#ifdef ENABLE_PERF
        std::cerr << format("[PerfCounter] %6d ms <%s>.\n", (int)timer.elapsed_ms(), name.c_str());
#endif
    }
};
/** rand **/
struct Xorshift {
    static constexpr uint32_t M = UINT_MAX;
    static constexpr double e = 1.0 / M;
    uint64_t x = 88172645463325252LL;
    Xorshift() {}
    Xorshift(uint64_t seed) { reseed(seed); }
    inline void reseed(uint64_t seed) { x = 0x498b3bc5 ^ seed; for (int i = 0; i < 20; i++) next_u64(); }
    inline uint64_t next_u64() { x ^= x << 7; return x ^= x >> 9; }
    inline uint64_t next_u64(uint64_t mod) { return next_u64() % mod; }
    inline uint64_t next_u64(uint64_t l, uint64_t r) { return l + next_u64(r - l + 1); }
    inline uint32_t next_u32() { return next_u64() >> 32; }
    inline uint32_t next_u32(uint32_t mod) { return ((uint64_t)next_u32() * mod) >> 32; }
    inline uint32_t next_u32(uint32_t l, uint32_t r) { return l + next_u32(r - l + 1); }
    inline double next_double() { return next_u32() * e; }
    inline double next_double(double c) { return next_double() * c; }
    inline double next_double(double l, double r) { return next_double(r - l) + l; }
};
/** shuffle **/
template<typename T> void shuffle_vector(std::vector<T>& v, Xorshift& rnd) { int n = v.size(); for (int i = n - 1; i >= 1; i--) { int r = rnd.next_u32(i); std::swap(v[i], v[r]); } }
/** split **/
std::vector<std::string> split(std::string str, const std::string& delim) { for (char& c : str) if (delim.find(c) != std::string::npos) c = ' '; std::istringstream iss(str); std::vector<std::string> parsed; std::string buf; while (iss >> buf) parsed.push_back(buf); return parsed; }
/** misc **/
template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T& val) { std::fill((T*)array, (T*)(array + N), val); } // fill array
template<typename T, typename ...Args> auto make_vector(T x, int arg, Args ...args) { if constexpr (sizeof...(args) == 0)return std::vector<T>(arg, x); else return std::vector(arg, make_vector<T>(x, args...)); }
template<typename T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template<typename T> bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
/** hash **/
namespace aux { template<typename T> inline void hash(std::size_t& s, const T& v) { s ^= std::hash<T>()(v) + 0x9e3779b9 + (s << 6) + (s >> 2); } }
namespace std { template<typename F, typename S> struct hash<std::pair<F, S>> { size_t operator()(const std::pair<F, S>& s) const noexcept { size_t seed = 0; aux::hash(seed, s.first); aux::hash(seed, s.second); return seed; } }; }
/** using **/
using ll = int64_t;
using ull = uint64_t;
using ld = double;
//using ld = boost::multiprecision::cpp_bin_float_quad;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;
template<typename T> using PQ = std::priority_queue<T>;
template<typename T> using MPQ = std::priority_queue<T, std::vector<T>, std::greater<T>>;

using namespace std;

template<typename T>
void print_vector(const std::vector<T>& v) {
    for (int i = 0; i < v.size(); i++) {
        std::cout << (i ? " " : "") << v[i];
    }
    std::cout << '\n';
}



#if 1
inline double get_temp(double stemp, double etemp, double t, double T) {
    return etemp + (stemp - etemp) * (T - t) / T;
};
#else
inline double get_temp(double stemp, double etemp, double t, double T) {
    return stemp * pow(etemp / stemp, t / T);
};
#endif



constexpr int N = 45, M = 50;
constexpr int64_t T = 500000000000000000;
std::array<int64_t, N> A, B;
std::array<int, M> us, vs, pus, pvs, bus, bvs;

void initialize() {
    cin >> A[0]; // ignore N
    for (int i = 0; i < N; i++) {
        cin >> A[i] >> B[i];
    }
    for (int i = 0; i < M; i++) {
        us[i] = 0;
        vs[i] = 1;
    }
}

void initialize(Xorshift& rnd) {
    for (int i = 0; i < N; i++) {
        A[i] = rnd.next_u64(100000000000000000, 1000000000000000000);
        B[i] = rnd.next_u64(100000000000000000, 1000000000000000000);
    }
    for (int i = 0; i < M; i++) {
        us[i] = 0;
        vs[i] = 1;
    }
}

double compute_score() {
    std::array<int64_t, N> CA(A), CB(B);
    for (int i = 0; i < M; i++) {
        int u = us[i], v = vs[i];
        CA[u] = CA[v] = (CA[u] + CA[v]) / 2;
        CB[u] = CB[v] = (CB[u] + CB[v]) / 2;
    }
    auto V1 = abs(T - CA[0]), V2 = abs(T - CB[0]);
    return 2e6 - 1e5 * log10(std::max(V1, V2) + 1.0);
}

double change_all(Xorshift& rnd) {
    double pscore = compute_score();
    pus = us; pvs = vs;
    for (int i = 0; i < M; i++) {
        us[i] = rnd.next_u32(N);
        do {
            vs[i] = rnd.next_u32(N);
        } while (us[i] == vs[i]);
    }
    double nscore = compute_score();
    return nscore - pscore;
}

double change_one(Xorshift& rnd) {
    double pscore = compute_score();
    pus = us; pvs = vs;
    int i = rnd.next_u32(M);
    us[i] = rnd.next_u32(N);
    do {
        vs[i] = rnd.next_u32(N);
    } while (us[i] == vs[i]);
    double nscore = compute_score();
    return nscore - pscore;
}


void solve() {

        Timer timer;
        Xorshift rnd;

#ifdef _MSC_VER
        initialize(rnd);
#else
        initialize();
#endif

        double score = compute_score();
        double best_score = -1.0;
        int loop = 0;
        double start_time = timer.elapsed_ms(), now_time, end_time = 900;
        while ((now_time = timer.elapsed_ms()) < end_time) {
            loop++;
            if (!(loop & 0x3FFFF)) {
                //dump(loop, score, best_score);
            }
            double diff = change_one(rnd);
            double temp = get_temp(100.0, 0.0, now_time - start_time, end_time - start_time);
            double prob = exp(diff / temp);
            if (prob < rnd.next_double()) {
                us = pus; vs = pvs;
            }
            else {
                score += diff;
                if (chmax(best_score, score)) {
                    bus = us;
                    bvs = vs;
                }
                //dump(score);
            }
        }
        dump(loop, score, best_score);


        us = bus;
        vs = bvs;
    cout << M << '\n';
    for (int i = 0; i < M; i++) {
        cout << us[i] + 1 << ' ' << vs[i] + 1 << '\n';
    }

}

int main() {

    int T = 1;
    //cin >> T;
    for (int t = 0; t < T; t++) {
        solve();
    }

    return 0;
}