#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

struct Point{ int x,y,num; };

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    cout << n/2 << '\n';
    vector<Point> a(n);
    rep(i,n){
        cin >> a[i].x >> a[i].y;
        a[i].num = i+1;
    }
    sort(all(a), [](Point a, Point b){
        int p = a.y*b.x, q = b.y*a.x;
        if(p!=q) return p < q;
        if(a.x!=b.x) return a.x < b.x;
        return a.y < b.y;
    });
    rep(i,n/2) cout << a[2*i].num << " " << a[2*i+1].num << '\n';
    return 0;
}