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(true){
        vector<pair<ld,ll>> rem;
        for (auto i : remS) {
            rem.push_back({atan2(xy[i].second-now.second,xy[i].first-now.first), i});
        }
        if(rem.size()==0)break;
        sort(rem.begin(),rem.end());
        auto it = lower_bound(rem.begin(),rem.end(),make_pair(last,-1ll));
        if(it==rem.end())it=rem.begin();
        auto [theta, ind] = *it;
        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;
    }
}