#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pint = pair<int, int>;
using pll = pair<ll, ll>;
using mint = map<int, int>;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
const char sp = ' ';
const char cmm = ',';
const int MOD = 1e9 + 7;
const int INF = 1e9;
const ll LINF = 1e18;
ll mod(ll a, ll b) { return (a % b + b) % b; }
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
void Yes() { cout << "Yes" << endl; }
void No() { cout << "No" << endl; }
void Judge(bool b) { b ? Yes() : No(); }
void YES() { cout << "YES" << endl; }
void NO() { cout << "NO" << endl; }
void JUDGE(bool b) { b ? YES() : NO(); }
ll powMod(ll b, ll e, ll m) {
  ll r = 1;
  while (e > 0) {
    if (e & 1) r = (r % m) * (b % m) % m;
    b = (b % m) * (b % m) % m;
    e >>= 1;
  }
  return r;
}
double distance(ll x1, ll y1, ll x2, ll y2) {
  return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}
template <class T>
bool chmax(T& a, const T& b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T& a, const T& b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T>
void ppp(T n) {
  cout << n << endl;
}
template <typename T1, typename T2>
ostream& operator<<(ostream& s, const pair<T1, T2>& p) {
  return s << "(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream& operator<<(ostream& s, const vector<T>& v) {
  int len = v.size();
  s << '[';
  for (int i = 0; i < len; ++i) {
    s << v[i];
    if (i < len - 1) s << ", ";
  }
  s << ']';
  return s;
}
struct aaa {
  aaa() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15);
  };
} fastio;
int main() {
  int n;
  cin >> n;
  if (n == 1) {
    ppp(1);
    ppp("1 1");
    return 0;
  }
  if (n == 2) {
    ppp(2);
    ppp("1 1");
    ppp("1 2");
    return 0;
  }
  int m = (n + 2) / 2;
  ppp(m);
  for (int i = 0; i < (m); ++i) {
    cout << 1 << sp << i + 1 << endl;
  }
  for (int i = 0; i < (n - m); ++i) {
    cout << i + 2 << sp << m << endl;
  }
  return 0;
}
