#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
const int FFTMOD = 1007681537;
const int INF = (int)1e9;
const long long LINF = (long long)1e18;
const long double PI = acos((long double)-1);
const long double EPS = 1e-9;
inline long long gcd(long long a, long long b) {
  long long r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
inline long long fpow(long long n, long long k, int p = MOD) {
  long long r = 1;
  for (; k; k >>= 1) {
    if (k & 1) r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T>
inline int chkmin(T& a, const T& val) {
  return val < a ? a = val, 1 : 0;
}
template <class T>
inline int chkmax(T& a, const T& val) {
  return a < val ? a = val, 1 : 0;
}
inline long long isqrt(long long k) {
  long long r = sqrt(k) + 1;
  while (r * r > k) r--;
  return r;
}
inline long long icbrt(long long k) {
  long long r = cbrt(k) + 1;
  while (r * r * r > k) r--;
  return r;
}
inline void addmod(int& a, int val, int p = MOD) {
  if ((a = (a + val)) >= p) a -= p;
}
inline void submod(int& a, int val, int p = MOD) {
  if ((a = (a - val)) < 0) a += p;
}
inline int mult(int a, int b, int p = MOD) { return (long long)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(long double x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(long double x, long double y) { return sign(x - y); }
struct HopcroftKarp {
  static const int MAXV = 1e6 + 5;
  static const int MAXE = 1e6 + 5;
  int nx, ny, E, adj[MAXE], nxt[MAXE], lst[MAXV], ptr[MAXV], lev[MAXV],
      que[MAXV], matx[MAXV], maty[MAXV];
  void init(int nx, int ny) {
    this->nx = nx, this->ny = ny;
    E = 0, fill_n(lst, nx, -1);
    fill_n(matx, nx, -1), fill_n(maty, ny, -1);
  }
  void add(int x, int y) { adj[E] = y, nxt[E] = lst[x], lst[x] = E++; }
  int bfs() {
    int qsize = 0;
    for (int x = 0; x < nx; x++)
      if (matx[x] != -1)
        lev[x] = 0;
      else {
        lev[x] = 1;
        que[qsize++] = x;
      }
    int found = 0;
    for (int i = 0; i < qsize; i++) {
      for (int x = que[i], e = lst[x]; ~e; e = nxt[e]) {
        int y = adj[e];
        if (!~maty[y])
          found = 1;
        else if (!lev[maty[y]]) {
          lev[maty[y]] = lev[x] + 1;
          que[qsize++] = maty[y];
        }
      }
    }
    return found;
  }
  int dfs(int x) {
    for (int& e = ptr[x]; ~e; e = nxt[e]) {
      int y = adj[e];
      if (!~maty[y] || (lev[maty[y]] == lev[x] + 1 && dfs(maty[y]))) {
        matx[x] = y;
        maty[y] = x;
        return 1;
      }
    }
    return 0;
  }
  int maxmat() {
    int res = 0;
    while (bfs()) {
      for (int x = 0; x < nx; x++) ptr[x] = lst[x];
      for (int x = 0; x < nx; x++)
        if (!~matx[x]) res += dfs(x);
    }
    return res;
  }
} hopkarp;
const int maxn = 1e5 + 5;
int n;
int lev[maxn];
int myrand() { return abs(rand() * rand() + 2311 * rand() + 1992); }
void chemthan() {
  srand(time(NULL));
  cin >> n;
  while (1.0 * clock() / CLOCKS_PER_SEC < 1.5) {
    hopkarp.init(n, n);
    int f[2] = {1, 0};
    vector<pair<int, int> > edges;
    for (int i = (1); i < (n); ++i) {
      int p = myrand() % i;
      edges.push_back(make_pair(p, i));
      lev[i] = lev[p] ^ 1;
      f[lev[i]]++;
      if (!(lev[p] & 1)) {
        hopkarp.add(p, i);
      } else {
        hopkarp.add(i, p);
      }
    }
    if (hopkarp.maxmat() != min(f[0], f[1])) {
      for (int i = (0); i < (n - 1); ++i) {
        cout << edges[i].first + 1 << " " << edges[i].second + 1 << "\n";
      }
      for (int i = (1); i < (n); ++i) {
        cout << 1 << " " << i + 1 << "\n";
      }
      return;
    }
  }
  cout << -1 << "\n";
  for (int i = (1); i < (n); ++i) {
    cout << 1 << " " << i + 1 << "\n";
  }
}
int main(int argc, char* argv[]) {
  ios_base::sync_with_stdio(0), cin.tie(0);
  if (argc > 1) {
    assert(freopen(argv[1], "r", stdin));
  }
  if (argc > 2) {
    assert(freopen(argv[2], "wb", stdout));
  }
  chemthan();
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}
