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

fn main() {
    let mut s: String = String::new();
    stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let a: Vec<i64> = (0..n)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();
    // 全部正か負にできれば累積和取れば良い
    let mut mn = 1 << 30;
    let mut mx = -(1 << 30);
    let mut mni = 0;
    let mut mxi = 0;
    for i in 0..n {
        if mn > a[i] {
            mn = a[i];
            mni = i;
        }
        if a[i] > mx {
            mx = a[i];
            mxi = i;
        }
    }

    let mut cnt = 0;
    let mut out = Vec::new();
    if mn == mx {
        println!("0");
        return;
    } else if mn.abs() > mx.abs() {
        for i in 0..n {
            if mni != i {
                cnt += 1;
                writeln!(out, "{} {}", mni + 1, i + 1).ok();
            }
        }
        for i in (1..n).rev() {
            cnt += 1;
            writeln!(out, "{} {}", i + 1, i).ok();
        }
    } else {
        for i in 0..n {
            if mxi != i {
                cnt += 1;
                writeln!(out, "{} {}", mxi + 1, i + 1).ok();
            }
        }
        for i in 1..n {
            cnt += 1;
            writeln!(out, "{} {}", i, i + 1).ok();
        }
    }
    println!("{}", cnt);
    stdout().write_all(&out).unwrap();
}