#include<iostream>
using namespace std;
int n,sol[1001],i;
#include<stdio.h>
#include<stdlib.h>
FILE *f,*g;
int valid(int k)
{
    for(i=1;i<k;i++)
        if(sol[i]==sol[k]||abs(sol[k]-sol[i])==abs(k-i))
        return 0;
    return 1;
}
int back(int k)
{
    if(k==n+1)
    {fprintf(g,"%d\n",k-1);
        for(i=1;i<k;i++)
            fprintf(g,"%d %d\n",i,sol[i]);
            exit(EXIT_SUCCESS);
    }
    else
    {
        sol[k]=0;
        while(sol[k]<n)
        {
            sol[k]++;
            if(valid(k))
                back(k+1);
        }
    }
}
int main()
{
    f=fopen("dame.in","r");
    g=fopen("dame.out","w");
    fscanf(f,"%d",&n);
    back(1);
}