#include<fstream.h>
ifstream f("dame.in");
ofstream g("dame.out");
int n,aux,c,r,i,x,a[1001];
int main()
{
f>>n;
if(n>=4)
{
r=n%12;
c=2;
if(r==3||r==9)
c=4;
i=0;
while(c<=n)
{
i++;
a[i]=c;
c=c+2;
}
if(r==3||r==9)
{
i++;
a[i]=2;
}
c=1;
x=i+1;
for(i=x;i<=n;i++)
{
a[i]=c;
c=c+2;
}
if(r==8)
for(i=x;i<n;i=i+2)
{
aux=a[i];
a[i]=a[i+1];
a[i+1]=aux;
}
if(r==2)
{
aux=a[x];
a[x]=a[x+1];
a[x+1]=aux;
for(i=x+2;i<=n-1;i++)
a[i]=a[i+1];
a[n]=5;
}
if(r==3||r==9)
{
for(i=x;i<=n-2;i++)
a[i]=a[i]+2;
a[n-1]=1;
a[n]=3;
}
g<<n<<'\n';
for(i=1;i<=n;i++)
g<<i<<" "<<a[i]<<'\n';
}
else
{
if(n==1||n==2)
g<<1<<'\n'<<"1 1"<<'\n';
if(n==3)
g<<2<<'\n'<<"1 1"<<'\n'<<"2 3"<<'\n';
}
f.close();
g.close();
return 0;
}