#include <bits/stdc++.h>
using namespace std;
const double pi = 3.14159265358979323846;
const double E = 2.7182818284590452354;
const struct _ {
  ios_base::Init i;
  int s;
  _() : s(ios_base::xalloc()) {
    srand(time(NULL));
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
  }
} _;
inline ostream& operator<<(ostream& o, const struct _&) {
  o.iword(_.s) = 0;
  return o << '\n';
}
template <class T>
inline ostream& operator,(ostream& o, const T& x) {
  if (o.iword(_.s))
    o << ' ';
  else
    o.iword(_.s) = 1;
  return o << x;
}
template <>
inline ostream& operator, <struct _>(ostream& o, const struct _&) {
  return o << _;
}
template <class I>
inline void in(I A, I B) {
  while (A != B) {
    cin >> *A;
    ++A;
  }
}
template <class I>
inline void out(I A, I B, char D = ' ') {
  if (A != B) {
    cout << *A;
    while (++A != B) {
      cout << D << *A;
    }
  }
  cout << _;
}
template <class T>
inline T sq(const T& X) {
  return X * X;
}
template <class T>
inline T power(T X, int Y) {
  assert(Y >= 0 && !(X == 0 && Y == 0));
  T R = (Y & 1) ? X : 1;
  while (Y >>= 1) {
    X *= X;
    if (Y & 1) R *= X;
  }
  return R;
}
int main() {
  int n, k;
  cin >> n >> k;
  if (n * k > n * (n - 1) / 2) {
    cout << -1 << _;
    return 0;
  }
  cout << n * k << _;
  for (int i = 0; i < n; i++) {
    for (int j = 1; j <= k; j++) {
      cout << i + 1 << " " << ((i + j) % n) + 1 << _;
    }
  }
}
