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

#ifdef HOME_
    #define DEBUG(x) x
#else
    #define DEBUG(x)
#endif
#define REP(x,n) for(int x=0;x<(n);++x)
#define FOREACH(x,n) for(__typeof(n.begin()) x = (n).begin(); x != (n).end(); ++x)

using namespace std;

#define LAST_V -100
#define NONE   -1

const int MAX_N = 102;
typedef pair<int,int> PII;

int n;
PII paths[MAX_N];

int main() {
	ios_base::sync_with_stdio(0);
	cin>>n;
	if (n==1) {
		cout << "2\n2 -1\n-1 -1";
		return 0;
	}
	int v = 1;
	while(n!=1) {
		if (n&1) {
			paths[v] = {LAST_V, v+1};
			--n;
			++v;
		}
		else {
			paths[v] = {v+1, v+2};
			paths[v+1] = {v+2, NONE};
			v += 2;
			n /= 2;
		}
	}
	paths[v] = {NONE, NONE};
	cout << v << endl;
	REP(x,v) {
		#define FIX(x) ((x)==LAST_V ? v : (x))
		cout << FIX(paths[x+1].first) << " " << FIX(paths[x+1].second) << endl;
	}
	return 0;
}