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#include <bits/stdc++.h>

using namespace std;

#define JOIN_(X, Y) X##Y
#define JOIN(X, Y) JOIN_(X, Y)
#define TMP JOIN(tmp, __LINE__)
#define PB push_back
#define SZ(x) int((x).size())
#define REP(i, n) for (int i = 0, TMP = (n); i < TMP; ++i)
#define FOR(i, a, b) for (int i = (a), TMP = (b); i <= TMP; ++i)
#define FORD(i, a, b) for (int i = (a), TMP = (b); i >= TMP; --i)

#ifdef DEBUG
#define DEB(x) (cerr << x)
#else
#define DEB(x)
#endif

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;

const int INF = 1e9 + 9;
const int MAX = 33;

void inline one() {
    int n;
    cin >> n;

    vector<pii> edges(2 * MAX + 3, pii(-1, -1));
    int last = SZ(edges) - 1;
    REP(i, MAX) {
        int up = i * 2 + 1;
        int left = i * 2 + 2;
        int down = i * 2 + 3;
        edges[up].first = left;
        edges[up].second = down;
        edges[left].second = down;
    }
    for (int i = 0, value = n; value > 0; ++i) {
        if (value % 2 == 1) {
            int left = i * 2 + 2;
            edges[left].first = last;
        }
        value /= 2;
    }

    cout << last << "\n";
    FOR(i, 1, last) { cout << edges[i].first << " " << edges[i].second << "\n"; }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    // int z; cin >> z; while(z--)
    one();
}