#include<fstream.h>

int main()
{
int n,i;
ifstream f ("dame.in");
ofstream g ("dame.out");
f>>n; f.close();
g<<n<<"\n";
g<<1<<' '<<n/2+n%2<<"\n";
for (i=2;i<=n;i++)
	if (i%2==0) if (i<n-1) g<<i<<' '<<n/2+n%2+i/2+1<<"\n";
					else g<<i<<' '<<n/2+n%2+1<<"\n";
		else g <<i<<' '<<n/2+n%2-i/2<<"\n";
g.close();
return 0;
}