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 argmin<T: cmp::Ord>(values: &Vec<T>) -> i32 {
    let min: &T = values.iter().min().unwrap();
    for i in 0..values.len() {
        if values[i] == *min {
            return i as i32;
        }
    }
    panic!("");
}

fn argmax<T: cmp::Ord>(values: &Vec<T>) -> i32 {
    let max: &T = values.iter().max().unwrap();
    for i in 0..values.len() {
        if values[i] == *max {
            return i as i32;
        }
    }
    panic!("");
}

fn read_line() -> String {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line).unwrap();
    return String::from(line.trim());
}

fn positive(values: Vec<i64>) -> () {
    let max = values.iter().max().unwrap();
    let max_index = argmax(&values);
    println!("{}", (values.len() - 1) * 2);
    for i in 0..values.len() {
        if i as i32 != max_index {
            println!("{} {}", max_index + 1, i + 1);
        }
    }
    for i in 0..values.len() - 1 {
        println!("{} {}", i + 1, i + 1 + 1);
    }
}

fn negative(values: Vec<i64>) -> () {
    let min = values.iter().min().unwrap();
    let min_index = argmin(&values);
    println!("{}", (values.len() - 1) * 2);
    for i in 0..values.len() {
        if i as i32 != min_index {
            println!("{} {}", min_index + 1, i + 1);
        }
    }
    for i in (0..values.len() - 1).rev() {
        println!("{} {}", i + 1 + 1, i + 1);
    }
}

fn main() {
    let n = read_line().parse::<i64>().unwrap();
    let values: Vec<i64> = read_line().split_whitespace().map(|v| v.parse::<i64>().unwrap()).collect();
    let min = values.iter().cloned().min().unwrap();
    let max = values.iter().cloned().max().unwrap();
    if 0 < min {
        positive(values);
    } else if max < 0 {
        negative(values);
    } else if -min < max {
        positive(values);
    } else {
        negative(values);
    }
}