#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;
vector < int > parents;
int computeMaxH(int x) {
int h = 0;
while (h * (h + 1) / 2 <= x)
h++;
return h - 1;
}
void generateTree(int maxH) {
parents.push_back(-1);
for (int i = 1; i <= maxH; ++i)
parents.push_back(i-1);
}
void printTree() {
printf("%d\n", (int)parents.size());
for (int i = 0; i < (int)parents.size(); ++i)
printf("%d %d\n", i, (int)parents[i]);
}
int main() {
//freopen("input","r",stdin);
//freopen("output","w",stdout);
int k; cin >> k;
int maxH = computeMaxH(k);
generateTree(maxH);
k -= maxH * (maxH + 1) / 2;
if (k > 0)
parents.push_back(k-1);
printTree();
return 0;
}
