#include<fstream.h>
int n,i=1,j=1;
int main()
{
ifstream f("dame.in");
ofstream g("dame.out");
f>>n;
g<<n<<'\n';

if(n%2==0)


 {   while((i+1)!=n)

       {g<<i<<" "<<j<<'\n';
	i+=2;j++;

       }

     g<<i<<" "<<j<<'\n';

     j++;

     g<<"2"<<" "<<j<<'\n';

     i++;j++;

     while(j<=n)

      {g<<i<<" "<<j<<'\n';
       i-=2;j++;
       }
  }

 else

  {
    while(i<=n)

     { g<<i<<" "<<j<<'\n';
      i+=2;j++;
     }

    j++;

    g<<"2"<<" "<<j<<'\n';

    j++;i--;

    while(j<=n)

     {g<<i<<" "<<j<<'\n';
      i-=2;j++;
     }
   }
f.close();
g.close();
return 0;
}