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#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;

#define FOR(i,a,b) for(int (i)=(int)(a); (i)!=(int)(b); ++(i))

struct Node {
    int id;
    Node *next_1, *next_2;
    Node(Node *n1 = 0, Node *n2 = 0):id(-1),next_1(n1),next_2(n2){}
};

int n, m;
vector<int> L(100, -1), R(100, -1);

void set_id(Node *node, int &current) {
    if (node->id != -1) return;
    node->id = current;
    ++current;
    if (node->next_1 != 0) { set_id(node->next_1, current); L[node->id] = node->next_1->id; }
    if (node->next_2 != 0) { set_id(node->next_2, current); R[node->id] = node->next_2->id; }
}

int main() {
    scanf("%d", &n);
    if (n == 1) {
        printf("2\n");
        printf("2 -1\n");
        printf("-1 -1\n");
        return 0;
    }

    vector<int> P;
    while (n>0) {
        P.push_back(n%2);
        n /= 2;
    }
    reverse(P.begin(), P.end());

    m = 1;
    Node *first = new Node();
    Node *last = first;
    FOR(i,1,P.size()) {
        Node *y = new Node();
        Node *x = new Node(y);
        last->next_1 = x;
        last->next_2 = y;
        last = y;
        m += 2;
        if (P[i] == 1) {
            first = new Node(first, x);
            ++m;
        }
    }

    int current = 1;
    last->id = m;
    set_id(first, current);
    printf("%d\n", m);
    FOR(i,0,m) printf("%d %d\n", L[i+1], R[i+1]);

}