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#include <bits/stdc++.h>
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define REP(i, a, b) for(int i = (a); i < (b); ++i)
#define TRAV(i, a) for(auto & i : (a))
#define SZ(x) ((int)(x).size())
#define PR std::pair
#define MP std::make_pair
#define X first
#define Y second
typedef long long ll;
typedef std::pair<int, int> PII;
typedef std::vector<int> VI;

int dag[1005][2];

int main(){
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);

	int k;
	std::cin >> k;

	int fre = 2;
	int head = 1;

	while(k > 1){
		if(k % 2 == 0){
			dag[head][0] = fre;
			dag[head][1] = fre+1;
			dag[fre][0] = fre+1;
			dag[fre][1] = -1;
			head = fre+1;
			fre += 2;
			k /= 2;
		}else{
			dag[head][0] = fre;
			dag[head][1] = -2;
			head = fre;
			fre++;
			k--;
		}
	}

	dag[head][0] = fre;
	dag[head][1] = -1;
	dag[fre][0] = -1;
	dag[fre][1] = -1;
	fre++;

	std::cout << fre-1 << "\n";
	REP(i, 1, fre) std::cout << dag[i][0] << " " << (dag[i][1] == -2 ? fre-1 : dag[i][1])<< "\n";

	return 0;
}