#include<fstream>
using namespace std;
int a[1001][1001],n,i,j,uz[1001];
int main()
{
	ifstream f("dame.in");
	ofstream g("dame.out");
	f>>n;
	if(n==1 || n==2)
		g<<1<<"\n"<<1<<" "<<1;
	if(n==3)
		g<<2<<"\n"<<1<<" "<<1<<"\n"<<3<<" "<<2;
	if(n>=4)
	{
		i=1;
		j=1;
		while(i<=n-1)
		{
			a[i][j]=1;
			i=i+2;
			j++;
			uz[i]=1;
		}
		i=n;
		j++;
		a[2][j-1]=1;
		while(j<=n)
		{
			a[i][j]=1;
			i=i-2;
			j++;
			uz[i]=1;
		}
		g<<n<<"\n";
		for(i=1;i<=n;i++)
		{
			for(j=1;j<=n;j++)
				if(a[i][j]==1)
					g<<i<<" "<<j<<"\n";
		}
	}
}