#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=2000000000000000000;
ll mod=998244353;
int main(){
    ll n;
    cin >> n;
    vector<tuple<ll,ll,ll>>t(n);
    for (ll i = 0; i < n; i++)
    {
        ll a,b;
        cin >> a >> b;
        t[i]={a,b,i};
    }
    sort(t.begin(),t.end());
    vector<ll>ans(n);
    for (ll i = 0; i < n; i++)
    {
        ans[i]=get<2>(t[i]);
    }
    cout << n/2 << endl;
    for (ll i = 0; i < n-n%2; i++)
    {
        cout << ans[i]+1 << ' ';
        if (i%2)
        {
            cout << endl;
        }
    }
}