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 C++14 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <numeric>
#include <cmath>

using namespace std;
using int64 = long long;
using P = pair<int64,int64>;

template <typename T> bool chmin(T& a, const T b) {if(a>b){a=b;return true;}return false;};
template <typename T> bool chmax(T& a, const T b) {if(a<b){a=b;return true;}return false;};

int main() {
    int64 n;
    cin >> n;
    vector<int64> a(n);
    int64 _max = INT_MIN;
    int64 _min = INT_MAX;
    int64 uindex = 0;
    int64 lindex = 0;
    for (int64 i=0; i<n; i++) {
        cin >> a[i];
        if (chmin(_min, a[i])) lindex = i+1;
        if (chmax(_max, a[i])) uindex = i+1;
    }

    vector<P> ans;
    bool r = _max < 0;

    if (signbit(_max) != signbit(_min)) {
        int64 index = uindex;
        if (abs(_max) < abs(_min)) {
            index = lindex;
            r = true;
        }

        for (int64 i=1; i<=n; i++) {
            if (i == index) continue;
            ans.emplace_back(i, index);
        }
    }

    int64 k = ans.size();

    for (int64 i=1; i<n; i++) {
        ans.emplace_back(i+1, i);
    }

    if (r) reverse(ans.begin() + k , ans.end());

    cout << ans.size() << endl;
    for (int i=0; i<ans.size(); i++) {
        if (i>k-1 && r)
            cout << ans[i].first << " " << ans[i].second << endl;
        else
            cout << ans[i].second << " " << ans[i].first << endl;
    }
}