Problem:
Score : 600 points

Problem Statement

Snuke has an integer sequence, a, of length N. The i-th element of a (1-indexed) is a_{i}.

He can perform the following operation any number of times:

Operation: Choose integers x and y between 1 and N (inclusive), and add a_x to a_y.

He would like to perform this operation between 0 and 2N times (inclusive) so that a satisfies the condition below. Show one such sequence of operations.
It can be proved that such a sequence of operations always exists under the constraints in this problem.

Condition: a_1 \leq a_2 \leq ... \leq a_{N}

Constraints

2 \leq N \leq 50

-10^{6} \leq a_i \leq 10^{6}

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_{N}

Output

Let m be the number of operations in your solution. In the first line, print m.
In the i-th of the subsequent m lines, print the numbers x and y chosen in the i-th operation, with a space in between.
The output will be considered correct if m is between 0 and 2N (inclusive) and a satisfies the condition after the m operations.

Sample Input 1

3
-2 5 -1

Sample Output 1

2
2 3
3 3

After the first operation, a = (-2,5,4).

After the second operation, a = (-2,5,8), and the condition is now satisfied.

Sample Input 2

2
-1 -3

Sample Output 2

1
2 1

After the first operation, a = (-4,-3) and the condition is now satisfied.

Sample Input 3

5
0 0 0 0 0

Sample Output 3

0

The condition is satisfied already in the beginning.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using Yorukatsu054.Questions;
using Yorukatsu054.Extensions;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace Yorukatsu054.Questions
{
    /// <summary>
    /// https://atcoder.jp/contests/arc086/tasks/arc086_b
    /// </summary>
    public class QuestionE : AtCoderQuestionBase
    {
        public override IEnumerable<object> Solve(TextReader inputStream)
        {
            var n = inputStream.ReadInt();
            var a = inputStream.ReadLongArray();

            var count = 0;
            var ops = new Queue<Operation>(2 * n);

            while (!Completed(a))
            {
                count++;
                ops.Enqueue(Add(a));
            }

            yield return count;
            foreach (var op in ops)
            {
                yield return op;
            }
        }

        bool Completed(long[] a)
        {
            for (int i = 0; i + 1 < a.Length; i++)
            {
                if (a[i] > a[i + 1])
                {
                    return false;
                }
            }

            return true;
        }

        int SearchMaxAbsIndex(long[] a)
        {
            long maxAbs = -1;
            int maxAbsIndex = -1;
            for (int i = 0; i < a.Length; i++)
            {
                if (Math.Abs(a[i]) > maxAbs)
                {
                    maxAbs = Math.Abs(a[i]);
                    maxAbsIndex = i;
                }
            }

            return maxAbsIndex;
        }

        Operation Add(long[] a)
        {
            var fromIndex = SearchMaxAbsIndex(a);
            long added = a[fromIndex];

            if (added > 0)
            {
                for (int toIndex = 1; toIndex < a.Length; toIndex++)
                {
                    if (a[toIndex - 1] > a[toIndex])
                    {
                        a[toIndex] += added;
                        return new Operation(fromIndex + 1, toIndex + 1);
                    }
                }
            }
            else
            {
                for (int toIndex = a.Length - 2; toIndex >= 0; toIndex--)
                {
                    if (a[toIndex] > a[toIndex + 1])
                    {
                        a[toIndex] += added;
                        return new Operation(fromIndex + 1, toIndex + 1);
                    }
                }
            }

            throw new Exception();
        }

        struct Operation
        {
            public int From { get; }
            public int To { get; }

            public Operation(int from, int to)
            {
                From = from;
                To = to;
            }

            public override string ToString() => $"{From} {To}";
        }
    }
}


namespace Yorukatsu054
{
    class Program
    {
        static void Main(string[] args)
        {
            IAtCoderQuestion question = new QuestionE();    // 問題に合わせて書き換え
            var answers = question.Solve(Console.In);
            foreach (var answer in answers)
            {
                Console.WriteLine(answer);
            }
        }
    }
}

#region Base Classes

namespace Yorukatsu054.Questions
{

    public interface IAtCoderQuestion
    {
        IEnumerable<object> Solve(string input);
        IEnumerable<object> Solve(TextReader inputStream);
    }

    public abstract class AtCoderQuestionBase : IAtCoderQuestion
    {
        public IEnumerable<object> Solve(string input)
        {
            var stream = new MemoryStream(Encoding.Unicode.GetBytes(input));
            var reader = new StreamReader(stream, Encoding.Unicode);

            return Solve(reader);
        }

        public abstract IEnumerable<object> Solve(TextReader inputStream);
    }

}

#endregion

#region Extensions

namespace Yorukatsu054.Extensions
{
    internal static class TextReaderExtensions
    {
        internal static int ReadInt(this TextReader reader) => int.Parse(ReadString(reader));
        internal static long ReadLong(this TextReader reader) => long.Parse(ReadString(reader));
        internal static double ReadDouble(this TextReader reader) => double.Parse(ReadString(reader));
        internal static string ReadString(this TextReader reader) => reader.ReadLine();

        internal static int[] ReadIntArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(int.Parse).ToArray();
        internal static long[] ReadLongArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(long.Parse).ToArray();
        internal static double[] ReadDoubleArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(double.Parse).ToArray();
        internal static string[] ReadStringArray(this TextReader reader, char separator = ' ') => reader.ReadLine().Split(separator);
    }
}

#endregion