#define _CRT_SECURE_NO_WARNINGS
#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    scanf("%d", &n);
    printf("%d\n", n / 2 + 1);
    int x = 1, y = 1;
	for (int i = 1; i <= n; i++) {
        printf("%d %d\n", x, y);
        (y == n / 2 + 1 ? x : y)++;
	}
    return 0;
    if (n & 1)
    {
        printf("%d\n", n / 2 + 1);
        for (int i = 1; i <= n / 2 + 1; i++)
            printf("%d %d\n", 1, i);
        for (int i = n / 2 + 1 + 1; i <= n; i++)
            printf("%d %d\n", i - n / 2 - 1, n / 2 + 1);
    }
    else
    {
        printf("%d\n", n / 2 + 1);
        for (int i = 1; i <= n / 2 + 1; i++)
            printf("%d %d\n", 1, i);
        for (int i = n / 2 + 1 + 1; i <= n; i++)
            printf("%d %d\n", i - n / 2 - 1, n / 2 + 1);
    }
    return 0;
    if (n == 1)
    {
        puts("1\n1 1");
        return 0;
    }
    printf("%d\n", ((n + 1) >> 1) + 1 - (n & 1));
    for (int i = 1; i <= n; i++)
        printf("%d %d\n", (i + 1) >> 1, ((i + 1) >> 1) + 1 - (i & 1));
    return 0;
}