typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
    ll n;
    std::cin >> n;
    vector<pair<ll,ll>> xy(n);
    vector<ll> ans;
    set<ll> remS;
    for (int i = 0; i < n; i++) {
        std::cin >> xy[i].first >> xy[i].second;
        if(xy[i].first==0&&xy[i].second==0){
            ans.push_back(i);
        }else{
            remS.insert(i);
        }
    }
    pair<ll,ll> now = {0,0};
    ld last = 0;
    while(remS.size()>0){
        set<pair<ld,ll>> rem;
        
        pair<ll,ll> L = {1e18,-1};
        pair<ll,ll> mi = {1e18,-1};
        for (auto i : remS) {
            ld t = atan2(xy[i].second-now.second,xy[i].first-now.first);
            if(t>last&&t<L.first){
                L.first = t;
                L.second =i;
            }
            if(mi.first>t){
                mi.first = t;
                mi.second = i;
            }
        }
        ld theta = L.second==-1 ? mi.first : L.first;
        ll ind = L.second==-1 ? mi.second : L.second;
        last = theta;
        remS.erase(ind);
        now = xy[ind];
        ans.push_back(ind);
    }
    std::cout << ans.size()/2 << std::endl;
    for (int i = 0; i < ans.size()/2; i++) {
        std::cout << ans[2*i]+1<<" "<<ans[2*i+1]+1 << std::endl;
    }
}