#include <cstdlib> #include <cctype> #include <cstring> #include <cstdio> #include <cmath> #include <algorithm> #include <vector> #include <string> #include <iostream> #include <sstream> #include <map> #include <set> #include <queue> #include <stack> #include <fstream> #include <numeric> #include <iomanip> #include <bitset> #include <list> #include <stdexcept> #include <functional> #include <utility> #include <ctime> #include <cassert> using namespace std; typedef long long LL; typedef unsigned long long ULL; #define MEM(a,b) memset((a),(b),sizeof(a)) const LL INF = 1e9 + 7; const int N = 1e5 + 10; int cross(const pair<int, int>& p1, const pair<int, int>& p2) { return p1.first * p2.second - p1.second * p2.first; } int main() { //freopen("input.txt", "r", stdin); //freopen("output.txt", "w", stdout); vector<pair<pair<int, int>, int>> vp; int n; scanf("%d", &n); for (int i = 1; i <= n; i++) { pair<int, int> p; scanf("%d%d", &p.first, &p.second); vp.emplace_back(p, i); } sort(vp.begin(), vp.end()); printf("%d\n", n / 2); for (int i = 0; i + 1 < n; i += 2) { printf("%d %d\n", vp[i].second, vp[i + 1].second); } return 0; }