using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using static System.Math;
using System.Text;
using System.Threading;
using System.Globalization;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using Library;

namespace Program
{
    public static class ProblemA
    {
        static bool SAIKI = false;
        static public int numberOfRandomCases = 0;
        static public void MakeTestCase(List<string> _input, List<string> _output, ref Func<string[], bool> _outputChecker)
        {
        }
        static public void Solve()
        {
            var N = (int)NN;
            var startTime = DateTime.Now;
            var AB = Range(0, N).Select(_ => new { idx = _, A = NN, B = NN }).ToArray();
            const long TGT = 500000000000000000;

            var operateList = new List<(int a, int b)>();
            var randomIdxList = Range(0, N).OrderByRand().ToArray();
            var randomIdxNextPickIdx = 0;
            Func<int> randomPick = () =>
            {
                var ret = randomIdxList[randomIdxNextPickIdx];
                if (++randomIdxNextPickIdx == N) randomIdxNextPickIdx = 0;
                return ret;
            };
            for (var i = 0; i < 40; ++i)
            {
                var a = randomPick();
                var b = randomPick();
                if (a == b) b = randomPick();
                operateList.Add((a, b));
            }
            Func<(double score, (int a, int b)[] added)> calcScoreFull = () =>
            {
                var tmp = new (long a, long b)[N];
                for (var i = 0; i < N; ++i)
                {
                    tmp[i].a = AB[i].A;
                    tmp[i].b = AB[i].B;
                }
                foreach (var item in operateList)
                {
                    var newa = (tmp[item.a].a + tmp[item.b].a) / 2;
                    var newb = (tmp[item.a].b + tmp[item.b].b) / 2;
                    tmp[item.a].a = tmp[item.b].a = newa;
                    tmp[item.a].b = tmp[item.b].b = newb;
                }
                var lastOpe = 50 - operateList.Count;
                var addOpe = new List<(int a, int b)>();
                var nowScore = Log10(Max(Abs(TGT - tmp[0].a), Abs(TGT - tmp[0].b)) + 1);
                for (var i = 0; i < lastOpe; ++i)
                {
                    var minScore = nowScore;
                    var minIdx = -1;
                    for (var j = 1; j < N; ++j)
                    {
                        var newa = (tmp[0].a + tmp[j].a) / 2;
                        var newb = (tmp[0].b + tmp[j].b) / 2;
                        var thisScore = Log10(Max(Abs(TGT - newa), Abs(TGT - newb)) + 1);
                        if (minScore > thisScore)
                        {
                            minScore = thisScore;
                            minIdx = j;
                        }
                    }
                    if (minIdx == -1) break;
                    addOpe.Add((0, minIdx));
                    tmp[0].a = tmp[minIdx].a = (tmp[0].a + tmp[minIdx].a) / 2;
                    tmp[0].b = tmp[minIdx].b = (tmp[0].b + tmp[minIdx].b) / 2;
                    nowScore = minScore;
                }
                return (nowScore, addOpe.ToArray());
            };
            var score = calcScoreFull().score;

            var TIME_LIMIT = 900;
            var startTemp = 1.0;
            var endTemp = 0.0;
            var loopCnt = 0;
            while (true)
            {
                ++loopCnt;
                //if (loopCnt % 1000 == 0)
                {
                    //Console.Error.WriteLine($"score:{score}");
                }
                var elapsed = (DateTime.Now - startTime).TotalMilliseconds;
                if (elapsed > TIME_LIMIT) break;
                var temp = startTemp + (endTemp - startTemp) * elapsed / TIME_LIMIT;

                var kakuritu = xorshift % 100;
                if (kakuritu < 20)
                {
                    // add
                    if (operateList.Count == 50) continue;
                    var a = randomPick();
                    var b = randomPick();
                    if (a == b) b = randomPick();
                    var pos = (int)(xorshift % (operateList.Count + 1));
                    operateList.Insert(pos, (a, b));
                    var newScore = calcScoreFull().score;

                    var diff = newScore - score;
                    var prob = Exp(-diff / temp);
                    if (prob * 10000000 > xorshift % 10000000)
                    {
                        score = newScore;
                    }
                    else
                    {
                        operateList.RemoveAt(pos);
                    }
                }
                else if (kakuritu < 40)
                {
                    // remove
                    if (operateList.Count == 0) continue;
                    var pos = (int)(xorshift % operateList.Count);
                    var removed = operateList[pos];
                    operateList.RemoveAt(pos);
                    var newScore = calcScoreFull().score;

                    var diff = newScore - score;
                    var prob = Exp(-diff / temp);
                    if (prob * 10000000 > xorshift % 10000000)
                    {
                        score = newScore;
                    }
                    else
                    {
                        operateList.Insert(pos, removed);
                    }
                }
                else if (kakuritu < 40)
                {
                    // swap
                    if (operateList.Count < 2) continue;
                    var pos1 = (int)(xorshift % operateList.Count);
                    var pos2 = (int)(xorshift % (operateList.Count - 1));
                    if (pos1 == pos2) ++pos2;
                    var old1 = operateList[pos1];
                    var old2 = operateList[pos2];
                    operateList[pos1] = old2;
                    operateList[pos2] = old1;
                    var newScore = calcScoreFull().score;

                    var diff = newScore - score;
                    var prob = Exp(-diff / temp);
                    if (prob * 10000000 > xorshift % 10000000)
                    {
                        score = newScore;
                    }
                    else
                    {
                        operateList[pos1] = old1;
                        operateList[pos2] = old2;
                    }
                }
                else
                {
                    // change
                    if (operateList.Count == 0) continue;
                    var a = randomPick();
                    var b = randomPick();
                    if (a == b) b = randomPick();
                    var pos = (int)(xorshift % operateList.Count);
                    var old = operateList[pos];
                    operateList[pos] = (a, b);
                    var newScore = calcScoreFull().score;

                    var diff = newScore - score;
                    var prob = Exp(-diff / temp);
                    if (prob * 10000000 > xorshift % 10000000)
                    {
                        score = newScore;
                    }
                    else
                    {
                        operateList[pos] = old;
                    }
                }
            }

            operateList.AddRange(calcScoreFull().added);
            Console.WriteLine(operateList.Count);
            foreach (var item in operateList)
            {
                Console.WriteLine($"{item.a + 1} {item.b + 1}");
            }
        }
        class Printer : StreamWriter
        {
            public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
            public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { base.AutoFlush = false; }
            public Printer(Stream stream, Encoding encoding) : base(stream, encoding) { base.AutoFlush = false; }
        }
        static LIB_FastIO fastio = new LIB_FastIODebug();
        static string[] args;
        static public void Main(string[] args_t) { args = args_t; if (args_t.Length == 0) { fastio = new LIB_FastIO(); Console.SetOut(new Printer(Console.OpenStandardOutput())); } if (SAIKI) { var t = new Thread(Solve, 134217728); t.Start(); t.Join(); } else Solve(); Console.Out.Flush(); }
        static long NN => fastio.Long();
        static double ND => fastio.Double();
        static string NS => fastio.Scan();
        static long[] NNList(long N) => Repeat(0, N).Select(_ => NN).ToArray();
        static double[] NDList(long N) => Repeat(0, N).Select(_ => ND).ToArray();
        static string[] NSList(long N) => Repeat(0, N).Select(_ => NS).ToArray();
        static long Count<T>(this IEnumerable<T> x, Func<T, bool> pred) => Enumerable.Count(x, pred);
        static IEnumerable<T> Repeat<T>(T v, long n) => Enumerable.Repeat<T>(v, (int)n);
        static IEnumerable<int> Range(long s, long c) => Enumerable.Range((int)s, (int)c);
        static IOrderedEnumerable<T> OrderByRand<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x, _ => xorshift);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x) => Enumerable.OrderBy(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderBy<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderBy(x.OrderByRand(), selector);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x) => Enumerable.OrderByDescending(x.OrderByRand(), e => e);
        static IOrderedEnumerable<T1> OrderByDescending<T1, T2>(this IEnumerable<T1> x, Func<T1, T2> selector) => Enumerable.OrderByDescending(x.OrderByRand(), selector);
        static IOrderedEnumerable<string> OrderBy(this IEnumerable<string> x) => x.OrderByRand().OrderBy(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderBy<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderBy(selector, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<string> OrderByDescending(this IEnumerable<string> x) => x.OrderByRand().OrderByDescending(e => e, StringComparer.OrdinalIgnoreCase);
        static IOrderedEnumerable<T> OrderByDescending<T>(this IEnumerable<T> x, Func<T, string> selector) => x.OrderByRand().OrderByDescending(selector, StringComparer.OrdinalIgnoreCase);
        static string Join<T>(this IEnumerable<T> x, string separator = "") => string.Join(separator, x);
        static uint xorshift { get { _xsi.MoveNext(); return _xsi.Current; } }
        static IEnumerator<uint> _xsi = _xsc();
        static IEnumerator<uint> _xsc() { uint x = 123456789, y = 362436069, z = 521288629, w = (uint)(DateTime.Now.Ticks & 0xffffffff); while (true) { var t = x ^ (x << 11); x = y; y = z; z = w; w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)); yield return w; } }
        static bool Chmax<T>(this ref T lhs, T rhs) where T : struct, IComparable<T> { if (lhs.CompareTo(rhs) < 0) { lhs = rhs; return true; } return false; }
        static bool Chmin<T>(this ref T lhs, T rhs) where T : struct, IComparable<T> { if (lhs.CompareTo(rhs) > 0) { lhs = rhs; return true; } return false; }
        static void Fill<T>(this T[] array, T value) => array.AsSpan().Fill(value);
        static void Fill<T>(this T[,] array, T value) => MemoryMarshal.CreateSpan(ref array[0, 0], array.Length).Fill(value);
        static void Fill<T>(this T[,,] array, T value) => MemoryMarshal.CreateSpan(ref array[0, 0, 0], array.Length).Fill(value);
        static void Fill<T>(this T[,,,] array, T value) => MemoryMarshal.CreateSpan(ref array[0, 0, 0, 0], array.Length).Fill(value);
    }
}
namespace Library {
    class LIB_FastIO
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public LIB_FastIO() { str = Console.OpenStandardInput(); }
        readonly Stream str;
        readonly byte[] buf = new byte[2048];
        int len, ptr;
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        byte read()
        {
            if (ptr >= len)
            {
                ptr = 0;
                if ((len = str.Read(buf, 0, 2048)) <= 0)
                {
                    return 0;
                }
            }
            return buf[ptr++];
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        char Char()
        {
            byte b = 0;
            do b = read();
            while (b < 33 || 126 < b);
            return (char)b;
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        virtual public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        virtual public long Long()
        {
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != '-' && (b < '0' || '9' < b));
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = (ret << 3) + (ret << 1) + b - '0';
            }
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        virtual public double Double() { return double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
    class LIB_FastIODebug : LIB_FastIO
    {
        Queue<string> param = new Queue<string>();
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        string NextString() { if (param.Count == 0) foreach (var item in Console.ReadLine().Split(' ')) param.Enqueue(item); return param.Dequeue(); }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public LIB_FastIODebug() { }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override string Scan() => NextString();
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override long Long() => long.Parse(NextString());
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public override double Double() => double.Parse(NextString());
    }
}