#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream f("harta.in");
ofstream g("harta.out");

vector<pair<int, int>> construieste_drumuri(int n, vector<pair<int, int>>& orase) {
    vector<pair<int, int>> drumuri;

    for (int i = 0; i < n; ++i) {
        for (int j = 1; j <= orase[i].first; ++j) {
            drumuri.push_back({i + 1, (i + j) % n + 1});
        }
    }

    return drumuri;
}

int main()
{

    int n;
    f >> n;

    vector<pair<int, int>> orase(n);
    for (int i = 0; i < n; ++i) {
        f >> orase[i].first >> orase[i].second;
    }

    vector<pair<int, int>> drumuri = construieste_drumuri(n, orase);

    g << drumuri.size() << endl;
    for (const auto& drum : drumuri) {
        g << drum.first << " " << drum.second << endl;
    }



    return 0;
}