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)

fn main() {
    let n = rv::<usize>()[0];
    let mut a = rv::<i32>();
    let mut c = Vec::with_capacity(n*2);
    let mut k=0;
    for i in 1..n {
        if a[k].abs()<a[i].abs() {
            k=i;
        }
    }
    if a[k]<0 {
        for i in (0..n-1).rev() {
            if a[i+1]<a[k] {k=i+1;}
            if a[i+1]>=a[i] {continue;}
            a[i]+=a[k]; c.push((k,i));
            if a[i+1]>=a[i] {continue;}
            for j in (i+1..n).rev() {
                if a[i+1]>=a[i]+a[j] {
                    a[i]+=a[j]; c.push((j,i));
                    break;
                }
            }
        }
    }
    else if a[k]>0 {
        for i in 1..n {
            if a[i-1]>a[k] {k=i-1;}
            if a[i-1]<=a[i] {continue;}
            a[i]+=a[k]; c.push((k,i));
            if a[i-1]<=a[i] {continue;}
            for j in 0..i {
                if a[i-1]<=a[i]+a[j] {
                    a[i]+=a[j]; c.push((j,i));
                    break;
                }
            }
        }
    }
    println!("{}",c.len());
    for (i,j) in c {
        println!("{} {}",i+1,j+1);
    }
}
fn rl() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s
}
fn rv<T>() -> Vec<T>
  where T: std::str::FromStr, T::Err: std::fmt::Debug, {
    rl().split_whitespace().map(|x|x.parse::<T>().unwrap()).collect()
}