bile

#include <fstream>

using namespace std;
ifstream f("bile.in");
ofstream g("bile.out");
long int n;

int main()
{
    f>>n;
    long int n1,n2,n3,n4;
    if(n%2==0)
    {
        n1=n/2,n2=n/2+2,n3=(3*n+2)/2,n4=(3*n+2)/2+1;
        while (n1>=1&&n3>=n+1)
            g<<n3<<' '<<n4<<'\n',--n3,++n4,g<<n1<<' '<<n2<<'\n',--n1,++n2;
        g<<n/2+1;
    }
    else
    {
        n1=n/2+1,n2=n/2+2,n3=(3*n+2)/2,n4=(3*n+2)/2+2;
        while (n1>=1&&n4<=2*n+1)
            g<<n1<<' '<<n2<<'\n',--n1,++n2,g<<n3<<' '<<n4<<'\n',--n3,++n4;
        g<<1<<' '<<n+1<<'\n';
        g<<(3*n+2)/2+1;
    }

    return 0;
}