1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
#pragma GCC optimize("Ofast")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define mp make_pair
#define eb emplace_back
#define pb push_back
#define e1 first
#define e2 second
#define uint unsigned int
#define ll long long
#define ull unsigned long long
#define ld long double
#define float long double
#define size(x) (int)x.size()
#define satori int testCases; cin>>testCases; while(testCases--)
#define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define all(r) begin(r),end(r)
#define time chrono::high_resolution_clock().now().time_since_epoch().count()
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
mt19937 rng(chrono::high_resolution_clock().now().time_since_epoch().count());
///////////////////
#define debug if(1)
///////////////////

const int MAXN=1e2+10;

pair<int,int> son[MAXN];
vector<pair<int,int>> lvl;

int32_t main()
{
	fastio;
	int k;
	cin>>k;
	int n=3;
	lvl.pb({2,3});
	int max_pow=1;
	while(max_pow*2<=k){
		lvl.pb({n+1,n+2});
		son[n+1]={n,n-1};
		son[n+2]={n,n-1};
		max_pow*=2;
		n+=2;
	}
	vector<int> levcon;
	for(int i=0;i<size(lvl);i++){
		if(k&(1<<i)){
			levcon.eb(i);
		}
	}
	if(size(levcon)&1)
		levcon.eb(-1);
	vector<int> concon;
	for(int i=0;i<size(levcon);i+=2){
		son[n+1]={lvl[levcon[i]].e1,(levcon[i+1]==-1?-1:lvl[levcon[i+1]].e1)};
		n++;
		concon.eb(n);
	}
	while(size(concon)>2){
		levcon.clear();
		if(size(concon)&1)
			concon.eb(-1);
		for(int i=0;i<size(concon);i+=2){
			son[n+1]={concon[i],concon[i+1]};
			n++;
			levcon.eb(n);
		}
		concon=levcon;
		levcon.clear();
		if(size(concon)&1)
			concon.eb(-1);
	}
	if(size(concon)&1)
		concon.eb(-1);
	son[1]={concon[0],concon[1]};
	son[2]={n+1,-1};
	son[3]={n+1,-1};
	n++;
	son[n]={-1,-1};
	cout<<n<<'\n';
	for(int i=1;i<=n;i++)
		cout<<son[i].e1<<' '<<son[i].e2<<'\n';
}