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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::cmp;

fn read_line() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).ok();
    buf
}

fn change_arr(arr: &mut Vec<i32>, x:usize, y:usize) {
    arr[y] += arr[x];
    println!("{} {}", x+1, y+1);
}



fn main() {
    let n = read_line().trim().parse::<usize>().expect("invalid");
    let mut arr:Vec<i32> = read_line().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mut max = 0;
    let mut idx = 0;
    for i in 0..n {
        if max < arr[i].abs() {
            max = arr[i].abs();
            idx = i;
        }
    }

    println!("{}", 2*n-1);

    for i in 0..n {
        change_arr(&mut arr, idx, i);
    }

    if arr[idx] < 0 {
        for i in (0..n-1).rev() {
            if arr[i+1] < arr[i] {
                change_arr(&mut arr, i+1, i);
            } else {
                change_arr(&mut arr, 0, 0);
            }
        }
    } else {
        for i in 0..n-1 {
            if arr[i+1] < arr[i] {
                change_arr(&mut arr, i, i+1);
            } else {
                change_arr(&mut arr, n-1, n-1);
            }
        }
    }
}