#include<iostream>
#include<vector>
#include<algorithm>//sort,二分探査など
//#include<bitset>
//#include<cmath>//pow,logなど
//#include<deque>
//#include<functional>
//#include<iterator>
//#include<map>
//#include<numeric>//gcd,lcm
//#include<queue>
//#include<set>
//#include<stack>
//#include<string>
//#include<utility>//pair

//QCFium法
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

//浮動小数点処理高速化
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

using namespace std;
using i64 = int64_t;
using f80 = __float80;
using u64 = uint_fast64_t;

constexpr i64 INF = 1010000000000000017LL;
constexpr u64 MOD = 1000000007LL;
constexpr f80 PI = 3.14159265358979323846;

#define _overload3(_1,_2,_3,name,...) name
#define repi(i,start,end) for(int i=(int)(start);i<(int)(end);++i)
#define _rep(i,n) repi(i,0,n)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define rrep(i,start,end) for(int i=(int)(start);i>(int)(end);--i)
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()

#define v(T) vector<T>
#define vv(T) v(v(T))
#define vvv(T) v(v(v(T)))
typedef v(int) vi;

#define show(x) cout<<#x<<" = "<<x<<endl;
#define PQ(T) priority_queue<T,v(T),greater<T> >

template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return true;}return false;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return true;}return false;}

template<typename T> ostream &operator<<(ostream &os, const vector< T > &v){
  rep(i,v.size()) os << v[i] << (i + 1 != v.size() ? " " : "");
  return os;
}
template<typename T> istream &operator>>(istream &is, vector< T > &v){
  for(T &in : v) is >> in;
  return is;
}

class modint {
public:
  u64 a;
  constexpr modint(const u64 x = 0) noexcept : a(x % MOD) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= MOD) a -= MOD;
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) a += MOD;
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % MOD;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    for(u64 exp = MOD - 2; exp; exp>>=1){
      if (exp % 2) *this *= rhs;
      rhs *= rhs;
    }
    return *this;
  }
  friend ostream& operator<<(ostream& os, const modint& m) {
    os << m.a;
    return os;
  }
};


i64 pow_mod(i64 n, i64 k, i64 m){
  i64 r = 1;
  for(;k;k>>=1){
    if(k&1) r=(r*n)%m;
    n=(n*n)%m;
  }
  return r;
}

struct uf{
  private:
    vi par, rank, size;
  public:
    uf(i64 n){ init(n); }
    void init(i64 n){
      par.resize(n);
      rank.resize(n,0);
      size.resize(n,1);
      rep(i,n) par[i] = i;
    }
    i64 root(i64 x){
      if(par[x] == x) return x;
      return par[x] = root(par[x]);
    }
    bool same(i64 x, i64 y){ return root(x) == root(y); }
    void unite(i64 x, i64 y){
      x = root(x), y = root(y);
      if(x==y) return;
      if(rank[x]==rank[y]) rank[x]++;
      if(rank[x]<rank[y]) swap(x,y);
      par[y] = x;
      size[x] += size[y];
    }
    i64 num(i64 x){ return size[root(x)]; }
};

//sort(rng(P),[](const vi &a, const vi &b){return a[1]<b[1];});

void Main()
{
  int N, K;
  cin >> N >> K;

  if(K > (N-1)*(N-2)/2) {
    cout << "-1\n";
    return;
  }

  int k = (N-1)*(N-2)/2 - K;
  int M = k + N - 1;

  cout << M << "\n";
  rep(i,1,N) {
    cout << "1 " << i+1 << "\n";
  }

  rep(i,1,N-1) {
    rep(j,i+1,N) {
      if(k>0) {
        cout << i+1 << " " << j+1 << "\n";
        k -= 1;
      }
    }
  }
}

int main()
{
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
//  cout << fixed << setprecision(15);
  Main();
}

Measured memory_bytes: 3644