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#include <cstdio>
#include <vector>
#include <string>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <utility>
using namespace std;

int main( )

{

long long k;
int w1,w2,w3,w4,w5,w6,w7,w8,w9,w10;
int p1,p2,p3,p4,p5,p6,p7,p8,p9,p10;
int ilew;

w1=2;
w2=3;
w3=5;
w4=6;
w5=6;
w6=7;
w7=9;
w8=7;
w9=7;
w10=9;

p1=0;
p2=2;
p3=4;
p4=6;
p5=5;
p6=7;
p7=9;
p8=6;
p9=4;
p10=9;


vector < pair <int,int> > g1; 
g1.push_back( make_pair(2,-1));
g1.push_back( make_pair(-1,-1));

vector< pair <int,int> > g2; 
g2.push_back( make_pair(2,3));
g2.push_back( make_pair(3,-1));
g2.push_back( make_pair(-1,-1));

vector< pair <int,int> > g3; 
g3.push_back( make_pair(2,3));
g3.push_back( make_pair(3,5));
g3.push_back( make_pair(4,-1));
g3.push_back( make_pair(5,-1));
g3.push_back( make_pair(-1,-1));

vector< pair <int,int> > g4; 
g4.push_back( make_pair(2,5));
g4.push_back( make_pair(3,4));
g4.push_back( make_pair(4,5));
g4.push_back( make_pair(5,-1));
g4.push_back( make_pair(6,-1));
g4.push_back( make_pair(-1,-1));

vector< pair <int,int> > g5; 
g5.push_back( make_pair(2,3));
g5.push_back( make_pair(3,4));
g5.push_back( make_pair(4,-1));
g5.push_back( make_pair(5,6));
g5.push_back( make_pair(6,-1));
g5.push_back( make_pair(-1,-1));

vector< pair <int,int> > g6; 
g6.push_back( make_pair(2,6));
g6.push_back( make_pair(3,4));
g6.push_back( make_pair(4,5));
g6.push_back( make_pair(5,-1));
g6.push_back( make_pair(6,-1));
g6.push_back( make_pair(7,-1));
g6.push_back( make_pair(-1,-1));

vector< pair <int,int> > g7; 
g7.push_back( make_pair(2,4));
g7.push_back( make_pair(3,7));
g7.push_back( make_pair(4,5));
g7.push_back( make_pair(5,6));
g7.push_back( make_pair(6,-1));
g7.push_back( make_pair(7,-1));
g7.push_back( make_pair(8,-1));
g7.push_back( make_pair(9,-1));
g7.push_back( make_pair(-1,-1));

vector< pair <int,int> > g8; 
g8.push_back( make_pair(2,3));
g8.push_back( make_pair(3,-1));
g8.push_back( make_pair(4,5));
g8.push_back( make_pair(5,-1));
g8.push_back( make_pair(6,7));
g8.push_back( make_pair(7,-1));
g8.push_back( make_pair(-1,-1));

vector< pair <int,int> > g9; 
g9.push_back( make_pair(2,3));
g9.push_back( make_pair(3,6));
g9.push_back( make_pair(4,5));
g9.push_back( make_pair(5,-1));
g9.push_back( make_pair(6,7));
g9.push_back( make_pair(7,-1));
g9.push_back( make_pair(-1,-1));

vector< pair <int,int> > g10; 
g10.push_back( make_pair(2,4));
g10.push_back( make_pair(3,7));
g10.push_back( make_pair(4,5));
g10.push_back( make_pair(5,6));
g10.push_back( make_pair(6,-1));
g10.push_back( make_pair(7,-1));
g10.push_back( make_pair(8,-1));
g10.push_back( make_pair(9,-1));
g10.push_back( make_pair(-1,-1));

cin >> k;





cout << w3 << endl;
for (int i=0; i<w3; i++)
  cout << g3[i].first << " " << g3[i].second << endl; 

  return 0;
}