#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
#include<vector>
#include<set>
#include<map>
#include<cmath>
using namespace std;
#define int long long 
#define endl "\n"
const int N = 9e5+10;
int n,m,k;
typedef pair<int,int> PII;
vector<int>g[N];

void solve()
{
    cin>>n;
    cout<<n*2<<endl;;
    int x= 1,y = 1;
    for(int i = 1;i <= 2*n;i ++)
    {
        cout<<i<<' '<<i<<endl;
    }
}
signed  main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);cout.tie(0);
   int t=1;
//   cin>>t;
   while(t--)
   {
       solve();
   }
    return 0;
}