#include <stdio.h>

using namespace std;
int n, tabla[1001];

int _valid(int x, int y)
{
    for (int i = 1; i < x; ++i) {
        if (tabla[i] == y)
            return 0;
        if (i != x) {
            if (i + tabla[i] == x + y)
                return 0;
            if (i - tabla[i] == x - y)
                return 0;
        }
    }
    return 1;
}

int _back(int x, int nr_d)
{
    if (nr_d == 0)
        return 1;

    for (int i = x; i <= n; ++i)
    for (int j = 1; j <= n; ++j) {
        if(_valid(i, j)) {
            tabla[i] = j;
            if(_back(i + 1, nr_d - 1))
                return 1;
        }
        tabla[i] = 0;
    }

    return 0;
}

int main()
{
    FILE * f = fopen("dame.in", "r");
    FILE * g = fopen("dame.out", "w");
    fscanf(f, "%d", &n);

    if (n == 2 || n == 3) {
        _back(1, n - 1);
        fprintf(g, "%d\n", n - 1);
    }
    else {
        _back(1, n);
        fprintf(g, "%d\n", n);
    }
    for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j)
        if (tabla[i] == j)
            fprintf(g, "%d %d\n", i, tabla[i]);
    return 0;
}