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)

#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn argmin<T>(u: &[T]) -> (usize)
where
    T: Copy + PartialOrd,
{
    assert!(u.len() != 0);

    let mut min_index = 0;
    let mut min = u[min_index];

    for (i, v) in u.iter().enumerate().skip(1) {
        if min > *v {
            min_index = i;
            min = *v;
        }
    }
    min_index
}

fn argmax<T>(u: &[T]) -> (usize)
where
    T: Copy + PartialOrd,
{
    assert!(u.len() != 0);

    let mut max_index = 0;
    let mut max = u[max_index];

    for (i, v) in u.iter().enumerate().skip(1) {
        if max < *v {
            max_index = i;
            max = *v;
        }
    }
    max_index
}

fn main() {
    let n: usize = read();
    let a = read_vec::<i64>();
    let a_min_idx = argmin(&a);
    let a_min = a[a_min_idx];
    let a_max_idx = argmax(&a);
    let a_max = a[a_max_idx];

    if a_min == a_max {
        println!("0");
        return;
    }

    println!("{}", 2 * n - 1);
    if a_max.abs() > a_min.abs() {
        for i in 0..n {
            println!("{0} {1}", a_max_idx + 1, i + 1);
        }
        for i in 1..n {
            println!("{0} {1}", i - 1 + 1, i + 1);
        }
    } else {
        for i in 0..n {
            println!("{0} {1}", a_min_idx + 1, i + 1);
        }
        for i in (0..n - 1).rev() {
            println!("{0} {1}", i + 1 + 1, i + 1);
        }
    }
}