#include <iostream>
#include <cstdio>
#include <cassert>
#include <cstring>
#include <vector>
#include <valarray>
#include <array>
#include <queue>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <cmath>
#include <complex>
#include <random>

using namespace std;
using ll = long long;
using ull = unsigned long long;
constexpr int TEN(int n) {return (n==0)?1:10*TEN(n-1);}

int main() {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        int d;
        cin >> d;
    }
    cout << n*(n-1)/2 << endl;
    for (int i = 0; i < n; i++) {
        for (int j = n-1; j-1 >= i; j--) {
            cout << j-1 << " " << j << endl;
        }
    }
    int d;
    cin >> d;
    return 0;
}