#include <bits/stdc++.h>
#pragma comment(linker, "/stack:225450978")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
const long long Mod = 1000000007LL, INF = 1e9, LINF = 1e18;
const long double Pi = 3.141592653589793116, EPS = 1e-9,
                  Gold = ((1 + sqrt(5)) / 2);
long long keymod[] = {1000000007LL, 1000000009LL, 1000000021LL, 1000000033LL};
long long keyCount = sizeof(keymod) / sizeof(long long);
template <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return __builtin_popcountll(s);
}
auto TimeStart = chrono::steady_clock::now();
auto TimeEnd = chrono::steady_clock::now();
void ControlIO(int argc, char* argv[]);
void TimerStart();
void TimerStop();
void Exit();
long long n, k;
vector<long long> Parent;
void Input() {
  cin >> n >> k;
  Parent.resize(n, -1);
}
void Solve() {
  set<pair<long long, long long> > Set;
  long long Petr = k + 1;
  for (long long i = 1; i <= k; i++) {
    Parent[i] = 0;
    Set.insert(make_pair(1LL, i));
  }
  while (Petr < n) {
    pair<long long, long long> z = *Set.begin();
    Set.erase(z);
    long long d = z.first, id = z.second;
    Parent[Petr] = id;
    Set.insert(make_pair(d + 1, Petr));
    Petr++;
  }
  long long maxDepth = Set.rbegin()->first;
  Set.erase(*Set.rbegin());
  maxDepth += Set.rbegin()->first;
  cout << maxDepth << '\n';
  for (long long i = 1; i < n; i++)
    cout << Parent[i] + 1 << " " << i + 1 << '\n';
}
int main(int argc, char* argv[]) {
  ControlIO(argc, argv);
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  Input();
  TimerStart();
  Solve();
  TimerStop();
  return 0;
}
void ControlIO(int argc, char* argv[]) {}
void TimerStart() {}
void TimerStop() {}
void Exit() {
  TimerStop();
  exit(0);
}
