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#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<map>

using namespace std;

typedef vector<int> VI;
typedef vector<vector<int> > VVI;
typedef long long LL;

#define FOR(x, b, e) for(int x=b; x<=(e); ++x)
#define FORD(x, b, e) for(int x=b; x>=(e); --x)
#define REP(x, n) for(int x=0; x<(n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second

int main() {
	ios_base::sync_with_stdio(0);
    int n;
    cin >> n;
    int size = 100;
    VVI graph(size);
    REP(i, size-1) {
        graph[i].PB(i+1);
    }
    int i = size - 1;
    int count = 2;
    while(count <= n) {
        i -= 2;
        graph[i].PB(i + 2);
        count *= 2;
    }
    if(count > n) {
        count /= 2;
    }
    n -= count;
    while(n > 0) {
        i--;
        int j = size - 1;
        count = 2;
        while(count <= n) {
            j -= 2;
            count *= 2;
        }
        graph[i].PB(j);
        n -= count > n ? count / 2 : count;
    }
    cout << size << '\n';
    REP(i, size) {
        if(graph[i].size() > 1) cout << graph[i][0] + 1 << ' ' << graph[i][1] + 1 << '\n';
        else if(graph[i].size() == 1) cout << graph[i][0] + 1 << " -1\n";
        else cout << "-1 -1\n";
    }
    return 0;
}