#include <iostream>
#include <vector>
#include <fstream>
using namespace std;

vector <pair<int, int> > dame;
int n; //int board[1001][1001];
ifstream f("dame.in");
ofstream g("dame.out");
void afisare(int board[1001][1001])
{
    g << n << endl; int i,j;
    for(i=0;i<dame.size();i++)
    {
        g << dame[i].first << " " << dame[i].second << endl;
    }

   /*  for (i=0;i<n;i++)
    {
        for (j=0;j<n;j++)
        {
            g << board[i][j] << " ";
        }
        g  << endl;
    }*/
}

int pairs(int board[1001][1001])
{
    int i,j;
    for (i=0;i<n;i++)
    {
        for (j=0;j<n;j++)
        {
            if (board[i][j]==1)
            {
                dame.push_back(make_pair(i,j));
            }
        }
    }
    afisare(board);
}
int checkIfSafe(int board[1001][1001],int i,int j)
{
    int it; int ii,ij;
    //cout << "s";
    for (it=i;it>=0;it--)
    {
        if (board[it][j]==1)
        {
            return false;
        }
    }
    ii=i;
    ij=j;
    //cout << "s";
    while(ii>=0 && ij>=0)
    {
        if (board[ii][ij]==1)
        {
            return false;
        }
        ii--;
        ij--;
    }
    ii=i;
    ij=j;
    while(ii>=0 && ij<=n)
    {
        if (board[ii][ij]==1)
        {
            return false;
        }
        ii--;
        ij++;
    }
    return true;


}
int solveNQ(int board[1001][1001], int i)
{
    //cout << "s";
    if (i==n)
    {
        return true;
    }
    //[i][j];
   // checkIfSafe();
   int j;
  // cout << "s";
    for (j=0;j<n;j++)
    {
        if (checkIfSafe(board,i,j))
        {
            board[i][j]=1;
            //solveNQ(board,i+1);
            if ( solveNQ(board, i+1) )
            //    cout << "h";
                return true;
            board[i][j]=0;
        }

    }
    return false;
}
int board[1001][1001];
int main()
{
    f >> n;
   // int board[1001][1001];
    int i,j;
    //cout << "s";
    for (i=0;i<n;i++)
    {
        for (j=0;j<n;j++)
        {
            board[i][j]=0;
        }
    }
    solveNQ(board,0);
    pairs(board);
  //  cout << board[0][2];
    return 0;
}