#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int n = 100, m = n * (n - 1) / 2;
  cout << m << endl;
  for (int i = 1; i < n; ++i) for (int j = i + 1; j <= n; ++j) cout << i << ' ' << j << endl;
}