#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using namespace boost::multiprecision;

# define REP(i,n) for (int i=0;i<(n);++i)
# define rep(i,a,b) for(int i=a;i<(b);++i)
# define all(v) v.begin(),v.end()
# define showVector(v) REP(i,v.size()){cout << (v[i]) << " ";} cout << endl;
template<class T> inline bool chmin(T &a, T b){ if(a > b) { a = b; return true;} return false;}
template<class T> inline bool chmax(T &a, T b){ if(a < b) { a = b; return true;} return false;}
typedef long long int ll;
typedef pair<ll,ll> P_ii;
typedef pair<double,double> P_dd;

template<class T>
using MaxHeap = std::priority_queue<T>;

template<class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template<class T>
vector<T> make_vec(size_t a){
    return vector<T>(a);
}

template<class T, class... Ts>
auto make_vec(size_t a, Ts... ts){
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template<typename T,typename V>
typename enable_if<is_class<T>::value==0>::type
fill_v(T &t,const V &v){t=v;}

template<typename T,typename V>
typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t,const V &v){
  for(auto &e:t) fill_v(e,v);
}

int pop_count(int n){
  return __builtin_popcount(n);
}

int pop_count(ll n){
  return __builtin_popcountll(n);
}

ll gcd(ll a, ll b) {
    if(a < b) swap(a,b);
    
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll a, ll b){
    ll g = gcd(a,b);
    return (a/g)*b;
}

// 素数判定 O(√n)
bool is_prime(ll n){
    if(n == 1) return false;
    for(ll i = 2; i * i <= n; i++){
        if(n % i == 0) return false;
    }
    return true;
}

// 約数列挙 O(√n)
vector<ll> divisor(ll n){
    vector<ll> res;
    for(ll i = 1; i * i <= n; i++){
        if(n % i == 0){
            res.push_back(i);
            if(i != n / i) res.push_back(n / i);
        }
    }
    return res;
}

template<typename T>
map<T, ll> prime_factorize(T x){
  map<T, ll> res;
  if(x == 0) return res;
  while(x%2==0){
    x/=2;
    res[2]++;
  }
  for(ll i=3;i*i<=x;i+=2){
    while(x%i==0){
      x/=i;
      res[i]++;
    }
  }
  if(x!=1) res[x]++;
  return res;
}

// エラトステネスの篩
// return lp[i] := iの最小素因数(lp[i] == iならば素数)
vector<int> SieveOfEratosthenes(int N = 10000000){
  vector<int> lp(N + 1, 0);
  vector<int> pr;
  for (int i=2; i<=N; ++i) {
      if (lp[i] == 0) {
          lp[i] = i;
          pr.push_back(i);
      }
      for (int j=0; j<(int)pr.size() && pr[j]<=lp[i] && i*pr[j]<=N; ++j)
          lp[i * pr[j]] = pr[j];
  }
  return lp;
}


// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x(x%mod){}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res+=a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res-=a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res*=a;
  }
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }
 
  // for prime mod
  mint inv() const {
    return pow(mod-2);
  }
  mint& operator/=(const mint a) {
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const {
    mint res(*this);
    return res/=a;
  }
};

const int MOD = 1000000007;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;

ll intceil(ll a, ll b){
    if(a < 0){
      a *= -1;
      b *= -1;
    }
    if(b >= 0) return (a + b - 1 ) / b;
    return a / b;
}

ll intfloor(ll a, ll b){
    if(a < 0){
      a *= -1;
      b *= -1;
    }
    if(b >= 0) return a / b;
    return (a - b + 1) / b;
}

void addM(ll &a, ll b) {
    a += b;
    if (a >= MOD) a -= MOD;
}

void mulM(ll &a, ll b) {
    a = ((a%MOD)*(b%MOD))%MOD ;
}

ll powM(ll a,ll b) {
    ll ret = 1;
    ll tmp = a;
    while(b>0) {
        if((b&1)==1) ret = (ret * tmp) % MOD;
        tmp = (tmp * tmp) % MOD;
        b = b >> 1;
    }
    return ret;
}

// mod. m での a の逆元 a^{-1} を計算する
ll modinv(ll a, ll m) {
    ll b = m, u = 1, v = 0;
    while (b) {
        ll t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= m;
    if (u < 0) u += m;
    return u;
}

// ラングレンス圧縮
vector<pair<char, int>> rang_com(string s){
  vector<pair<char, int>> ret;
  string t = s;
  t.erase(unique(all(t)), t.end());
  int now = 0;
  int pre = 0;
  for(auto ct : t){
    while(now < s.size() && s[now] == ct) now++;
    if(ret.size() == 0){
      ret.push_back({ct, now});
    } else {
      ret.push_back({ct, now - pre});
    }
    pre = now;
  }
  return ret;
}

ll mypow(ll a, ll t) {
  if (!t) return 1;
  ll ret = mypow(a, t>>1);
  ret *= ret;
  if (t&1) ret *= a;
  return ret;
}

struct LazySegmentTree{
private:
   int n;
   vector<ll> node,lazy;
public:
   LazySegmentTree(int sz,ll init=0){
      n=1;
      while(n<sz)n*=2;
      node.resize(2*n-1,init);
      lazy.resize(2*n-1,0);
   }
 
   void eval(int k,int l,int r){
      if(lazy[k]!=0)node[k]+=lazy[k];
      if(r-l>1){
          lazy[2*k+1]+=lazy[k];
          lazy[2*k+2]+=lazy[k];
      }
      lazy[k]=0;
   }
      //[a,b)にxを加算
   void add(int a,int b,ll x,int k=0,int l=0,int r=-1){
       if(r<0)r=n;
       eval(k,l,r);
       if(r<=a||b<=l)return;
       if(a<=l&&r<=b){
          lazy[k]+=x;
          eval(k,l,r);
       }
       else {
          add(a,b,x,2*k+1,l,(l+r)/2);
          add(a,b,x,2*k+2,(l+r)/2,r);
          node[k]=max(node[2*k+1],node[2*k+2]);
          // node[k]=min(node[2*k+1],node[2*k+2]);
        }
   }
   //[a,b)でのminを返す
   ll get(int a,int b,int k=0,int l=0,int r=-1){
      if(r<0)r=n;
      eval(k,l,r);
      if(r<=a||b<=l)return 0;
//      if(r<=a||b<=l)return longinf;
      if(a<=l&&r<=b)return node[k];
      ll xl=get(a,b,2*k+1,l,(l+r)/2);
      ll xr=get(a,b,2*k+2,(l+r)/2,r);
      return max(xl,xr);
//      return min(xl,xr);
   }
};

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);  

  int N, K;
  cin >> N >> K;

  vector<pair<int, int>> ans;
  for(int i = 2; i <= N; i++){
    ans.push_back({1, i});
  }

  if(K > (N-1)*(N-2)/2){
    cout << -1 << endl;
    return 0;
  }

  int now = 0;
  for(int i = 2; i <= N; i++){
    int num = N - i;
    if(now == K){
      for(int j = i + 1; j <= N; j++) {
        ans.push_back({i, j});
      }
    } else if(now + num >= K){
      for(int j = i + 1 + (K - now); j <= N; j++) {
        ans.push_back({i, j});
      }
      now = K;
    } else {
      now += num;
    }
  }

  cout << ans.size() << "\n";
  for(auto a : ans){
    cout << a.first << " " << a.second << "\n";
  }
  
  return 0;
}

Measured memory_bytes: 384