#include <bits/stdc++.h>

using namespace std;

ifstream fin("dame.in");
ofstream fout("dame.out");

vector<pair<int, int> > afis;
const int NMAX(1005);
bool mat[NMAX][NMAX], lib2[NMAX], lib[NMAX];
int n;
void mark(int x, int y)
{
    int cx = x, cy = y;
    while(cx <= n && cy <= n)
        mat[cx][cy] = 1, ++cx, ++cy;
    cx = x, cy = y;
    while(cx >= 1 && cy >= 1)
        mat[cx][cy] = 1, --cx, --cy;
    cx = x, cy = y;
    while(cx <= n && cy >= 1)
        mat[cx][cy] = 1, ++cx, --cy;
    cx = x, cy = y;
    while(cx >= 1 && cy <= n)
        mat[cx][cy] = 1, --cx, ++cy;
}
int main()
{
    fin >> n;
    int i, j;
    if(n % 2 == 1)
        i = n, j = 1;
    else i = n - 1, j = 1;
    afis.push_back({i, j});
    mark(i, j);
    lib2[i] = 1;
    lib[j] = 1;
    while(i != 1)
    {
        i -= 2;
        j++;
        afis.push_back({i, j});
        mark(i, j);
        lib[j] = 1;
        lib2[i] = 1;
    }
    for(int x = n; x >= 1; --x)
        if(!lib2[x])
        {
            int y = j;
            while(y <= n && (lib[y] == 1 || mat[x][y] == 1))
                ++y;
            if(y <= n)
            {
                lib[y] = 1;
                afis.push_back({x, y});
            }
        }
    fout << afis.size() << '\n';
    for(auto it: afis)
        fout << it.first << ' ' << it.second << '\n';
    return 0;
}