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 Ruby (2.3.3) (judge verdict: Accepted)

def setmax(n,arr,ans)
  1.upto(n-1) do |ii|
    abs = arr[ii-1] - arr[ii]
    if abs > 0
      arr[ii] += arr[ii-1]
      ans.push([ii,ii+1])
    end
  end
end
def setmin(n,arr,ans)
  (n-2).downto(0) do |ii|
    abs = arr[ii] - arr[ii+1]
    if abs > 0
      arr[ii] += arr[ii+1]
      ans.push([ii+2,ii+1])
    end
  end
end
n = gets.chomp.to_i
arr = gets.chomp.split.map{ |item| item.to_i}
ans = []
min = arr.min
mini = arr.index(min)
max = arr.max
maxi = arr.index(max)
list = []
n.times do |i|
  list.push([i,arr[i]])
end
list.sort!{ |a,b| a[1] <=> b[1]}

if min >= 0
  setmax(n,arr,ans)
elsif max <= 0
  setmin(n,arr,ans)
else
  if (max.abs - min.abs) >= 0
    n.times do |ii|
      if arr [ii] <= 0
        jj = list.select{ |item| (item[1] + arr[ii]) >= 0}[0]
        arr[ii] += jj[1]
        ans.push([jj[0]+1,ii+1])
      end
    end
    setmax(n,arr,ans)
  else
    n.times do |ii|
      if arr [ii] >= 0
        jj = list.select{ |item| (item[1] + arr[ii]) <= 0}[-1]
        arr[ii] += jj[1]
        ans.push([jj[0]+1,ii+1])
      end
    end
    setmin(n,arr,ans)
  end
end
print ans.size,"\n"
ans.each do |one|
  print one[0]," ",one[1],"\n"
end