#include <bits/stdc++.h>
using namespace std;
using pii=pair<int,int>;
using tii=tuple<int,int,int>;
using qii=tuple<int,int,int,int>;
using ll=long long;
using ld=long double;
const ll INF=1ll<<60;
#define rep(i,n) for (int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
template<class T> inline bool chmin(T &a,T b){
    if(a>b){
        a=b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T &a,T b){
    if(a<b){
        a=b;
        return true;
    }
    return false;
}
auto program_start=chrono::system_clock::now();
mt19937 mt;
int rand_int(int r){    //[0,r)
    return mt()%r;
}
int rand_int(int l,int r){  //[l,r)
    return l+mt()%(r-l);
}
double rand_double(){   //[0.0,1.0]
    return (double)mt()/(double)mt19937::max();
}
const ll C=5e17;
int N;
vector<ll> A,B;
namespace Solver{
    int score(vector<pii> &ans){
        vector<ll> a=A,b=B;
        for(auto [u,v]:ans){
            a[v]=a[u]=(a[u]+a[v])/2;
            b[v]=b[u]=(b[u]+b[v])/2;
        }
        return floorl(2000000.0-100000.0*log10l(max(abs(C-a[0]),abs(C-b[0]))+1));
    }
    void solve(){
        vector<pii> ans;
        int pre_score=score(ans);
        int cnt=0;
        int max_score=0;
        vector<pii> max_score_ans;
        while(true){
            auto now=chrono::system_clock::now();
            int ms=chrono::duration_cast<chrono::milliseconds>(now-program_start).count();
            if(950<=ms) break;
            vector<pii> new_ans=ans;
            int r=mt()%3;
            int x=rand_int(N),y=rand_int(N);
            if(x==y) continue;
            if(y<x) swap(x,y);
            if(new_ans.empty()||((int)new_ans.size()<50&&r==0)){
                int d=rand_int((int)new_ans.size()+1);
                new_ans.insert(new_ans.begin()+d,{x,y});
            }else if(r==1){
                int d=rand_int((int)new_ans.size());
                new_ans.erase(new_ans.begin()+d);
            }else{
                int d=rand_int((int)new_ans.size());
                new_ans[d]={x,y};
            }
            cnt++;
            int new_score=score(new_ans);
            if(pre_score<=new_score){
                if(pre_score<new_score){
                    cnt=0;
                    if(chmax(max_score,new_score)){
                        max_score_ans=new_ans;
                    }
                }
                pre_score=new_score;
                ans=new_ans;
            }
            if(cnt==10000){
                ans.clear();
                pre_score=score(ans);
                cnt=0;
            }
        }
        cout << (int)max_score_ans.size() << '\n';
        for(auto [u,v]:max_score_ans) cout << u+1 << ' ' << v+1 << '\n';
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> N;
    A.resize(N);
    B.resize(N);
    rep(i,N) cin >> A[i] >> B[i];
    Solver::solve();
}