# include <bits/stdc++.h>

using namespace std;

namespace kh {
  template <typename T>
    constexpr T& cmin(T& a, T const& b)
    { return a = ::std::min(a, b); }
  template <typename T>
    constexpr T& cmax(T& a, T const& b)
    { return a = ::std::max(a, b); }
  constexpr int Nn(1'900);
  constexpr int Nx(2'000);
  constexpr int K(15);
  vector<pair<int, int>> ans;
  namespace sol2 {
    void slv(int const l, int const r) {
      if (r - l <= 1) return;
      int const m((l + r) / 2);
      for (int i(l); i != m - 1; ++i) ans.emplace_back(i, m);
      for (int i(r); i != m + 1; --i) ans.emplace_back(m, i);
      slv(l, m - 1), slv(m + 1, r);
    }
    void main(int const n) { slv(0, n); }
  }
  namespace sol3 {
    int f[Nx + 1];
    int g[Nx + 1];
    int h[Nx + 1];
    void init(int const n) {
      double rat(0);
      for (int i(4), j(2), k(j - 1); i <= n; ++i) {
        f[i] = i - 2;
        f[i] += f[(i + 0) / 2 - 1];
        f[i] += f[(i + 1) / 2 - 1];
        g[i] = 1, h[i] = 0;
        auto const val = [&] (int const j, int const k) {
          int const q0(k / (j - 1)), q1(q0 + 1);
          int const r1(k % (j - 1)), r0(j - 1 - r1);
          int res(j * (j - 1) / 2);
          res -= (q0 == 1 ? r0 : 0);
          res += f[max(q0 - 2, 0)] * r0;
          res += f[max(q1 - 2, 0)] * r1;
          res += f[(i - k + 0) / 2 - 1];
          res += f[(i - k + 1) / 2 - 1];
          res += 2 * max(q0 - 2, 0) * r0;
          res += 2 * max(q1 - 2, 0) * r1;
          res += (i - k) - 2;
          return res;
        };
        auto const chk = [&] (int const dj, int const dk) {
          if (j + dj < 2) return false;
          if (j + dj >= i - 0) return false;
          if (k + dk >= i - 1) return false;
          if (k + dk < j + dj - 1) return false;
          if (val(j + dj, k + dk) >= val(j, k)) return false;
          else return j += dj, k += dk, true;
        };
        while (true) {
          bool ok(false);
          for (int i(-7); i <= +7; ++i)
            for (int j(-7); j <= +7; ++j)
              ok = chk(i, j) || ok;
          if (ok) continue;
          else break;
        }
        if (val(j, k) < f[i])
          f[i] = val(j, k), g[i] = j, h[i] = k;
        // fprintf(stderr, "%i %i %i %i\n", i, f[i], g[i], h[i]);
        cmax(rat, 1.0 * f[i] / i);
      }
    }
    void slv(int const l, int const r) {
      if (r - l <= 3) return;
      int const gg(g[r - l]);
      int const hh(h[r - l]);
      if (gg == 1) {
        int const m((l + r) / 2);
        for (int i(l); i != m - 1; ++i) ans.emplace_back(i, m);
        for (int i(r); i != m + 1; --i) ans.emplace_back(m, i);
        slv(l, m - 1), slv(m + 1, r);
      } else {
        vector<int> p(1, l);
        p.push_back(l + (r - l - hh) / 2);
        for (int i(gg - 1), j(hh); i; --i)
          p.push_back(p.back() + j / i), j -= j / i;
        p.push_back(r);
        if (r - l - hh > 3) ans.emplace_back(p.front(), *next(p.begin()));
        if (r - l - hh > 2) ans.emplace_back(*prev(p.end(), 2), p.back());
        for (auto i(next(p.begin())); next(i) != p.end(); advance(i, 1))
          for (auto j(next(p.begin())); j != i; advance(j, 1))
            if (*i - *j != 1) ans.emplace_back(*j, *i);
        for (auto i(next(p.begin())); i != p.end(); advance(i, 1)) {
          int const ll(*prev(i, 1)), rr(*prev(i, 0));
          for (int j(ll + 1); j != rr; ++j) {
            if (ll != l && j - ll > 1) ans.emplace_back(ll, j);
            if (rr != r && rr - j > 1) ans.emplace_back(j, rr);
          }
        }
        slv(p.front(), *next(p.begin()) - 1);
        slv(*prev(p.end(), 2) + 1, p.back());
        for (auto i(next(p.begin(), 2)); next(i) != p.end(); advance(i, 1))
          slv(*prev(i) + 1, *i - 1);
      }
    }
    void main(int const n) {
      init(n), slv(0, n);
      assert(int(ans.size()) == f[n]);
    }
  }
  void main() {
    int n, k;
    cin >> n >> k;
    switch (k) {
      case 2 : sol2::main(n); break;
      case 3 : sol3::main(n); break;
    }
    cout << ans.size() << '\n';
    for (auto const [i, j] : ans)
      cout << i << ' ' << j << '\n';
  }
}

int main() { kh::main(); }