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

/***** type *****/
using ll = long long;
using ld = long double;
using ml = boost::multiprecision::cpp_int;
using md = boost::multiprecision::cpp_dec_float_100;
template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;
template <class T> using vvvt = vector<vector<vector<T>>>;
template <class T> using uset = unordered_set<T>;
template <class T1, class T2> using umap = unordered_map<T1, T2>;

/***** define *****/
#define all(c) (c).begin(), (c).end()            // begin to end
#define coutld cout << fixed << setprecision(10) // cout long double
#define rep(i, b, e) for (ll i = b; i < e; i++)  // repeat
#define repr(i, b, e) for (ll i = b; e < i; i--) // repeat reverse
#define pair NyaaPair                            // nyaa pair
#define first f                                  // pair::first
#define second s                                 // pair::second
/***** const value *****/
#define llong_max 9223372036854775807            // 9 * 10^18
#define ldbl_max 1.79769e+308                    // 1.7 * 10^308
#define pi 3.1415926535897932                    // 3.14 ...
#define loop_end 9223372036854775806             // LLONG_MAX-1
/***** for each macro *****/
#define fori(i, ...) if(ll i = -1) for(__VA_ARGS__) if(i++, true)
#define each(i, e, c) fori(i, auto& e: c)
#define forir(i, v, ...) if(ll i=(ll)v.size())for(__VA_ARGS__)if(i--,true)
#define eachr(i, e, c) forir(i, auto e = c.rbegin(); e != c.rend(); ++e)

/***** lambda *****/
auto Count = [] // long long count value
(auto b, auto e, auto x) { return (ll)count(b, e, x); };
auto CtoL = [] // char to number
(auto c) { return (ll)(c - '0'); };
auto CeilD = [] // long double ceiling div
(auto a, auto b) { return ceil((ld)a / (ld)b); };
auto Fix = [] // fix value
(auto b, auto e, auto fix)
{ for (auto it = b; it != e; ++it) *it += fix; };
auto LtoC = [] // number to char
(auto n) { return (char)('0' + n); };
auto Pow = [] // long long pow
(auto a, auto b) { return (ll)pow(a, b); };
auto Pow2 = [] // long long pow2
(auto n) { return (1LL << n); };
auto Pow10 = [] // long long pow10
(auto n) { return (ll)pow(10, n); };
auto Size = []  // long long collection size
(auto& c) { return (ll)(c).size(); };
auto Sum = [] // long long accumulate
(auto b, auto e) { return accumulate(b, e, 0LL); };

/***** template *****/
template <class T> void MakeVVT
(ll ys, ll xs, vvt<T>& v, T fill = T())
{	// vector<vector<T>> resize + fill
	v.resize(ys); rep(y, 0, ys) v[y].resize(xs, fill);
}
template <class T> void MakeVVVT
(ll zs, ll ys, ll xs, vvvt<T>& v, T fill = T())
{	// vector<vector<vector<T>>> resize + fill
	v.resize(zs); rep(z, 0, zs) MakeVVT(ys, xs, v[z], fill);
}
template <class T> void InputVT
(ll xs, vt<T>& v, T fix = T())
{	// input vector<T> (T != struct) + fix
	v.resize(xs); rep(i, 0, xs) { cin >> v[i]; v[i] += fix; }
}
template <class T> void InputVVT
(ll ys, ll xs, vvt<T>& v, T fix = T())
{	// input vector<vector<T>> (T != struct) + fix
	MakeVVT(ys, xs, v, fix);
	rep(y, 0, ys) rep(x, 0, xs) { cin >> v[y][x]; v[y][x] += fix; }
}
template <class T> void InputVVVT
(ll zs, ll ys, ll xs, vvvt<T>& v, T fix = T())
{	// input vector<vector<vector<T>>> (T != struct) + fix
	v.resize(zs); rep(z, 0, zs) InputVVT(ys, xs, v[z], fix);
}
template <class T1, class T2> struct NyaaPair
{	// nyaa pair template
	T1 f; T2 s;
};
template <class T1, class T2> bool
operator < (const NyaaPair<T1, T2>& l, const NyaaPair<T1, T2>& r)
{	// nyaa pair template operator <
	return (l.f != r.f) ? l.f < r.f : l.s < r.s;
}
template <class T1, class T2> bool
operator > (const NyaaPair<T1, T2>& l, const NyaaPair<T1, T2>& r)
{	// nyaa pair template operator >
	return (l.f != r.f) ? l.f > r.f : l.s > r.s;
}

/**************************************/
/********** BEGIN OF NYA LIB **********/
/**************************************/

namespace NyaGadget {}

namespace NyaGadget
{	/***** 数え上げライブラリ *****/

	template< typename T > struct NT_Counting
	{	// 引数にModライブラリを渡すことも可能

		static T P(long long n, long long r)
		{
			if (r < 0 || n < r) return 0;

			T res = 1;
			for (long long i = n; n - r < i; i--) res *= i;
			return res;
		}

		static T C(long long n, long long r)
		{
			if (r < 0 || n < r) return 0;

			T res = 1;
			for (long long i = n; n - r < i; i--) res *= i;
			for (long long i = r; 0 < i; i--) res /= i;
			return res;
		}

		static T H(long long n, long long r)
		{
			if (n < 0 || r < 0) return 0;
			return (r == 0) ? 1 : C(n + r - 1, r);
		}

		static T Catalan(long long n)
		{
			return C(2 * n, n) - C(2 * n, n - 1);
		}

		/**
		@brief 累乗の計算
		@note
		 繰り返し自乗法でxのn乗を返す。計算量O(logN)
		**/
		static T Pow(long long x, long long n)
		{
			T res = 1;
			if (0 < n)
			{
				res = Pow(x, n / 2);
				res = res * res;
				if (n % 2 != 0) res *= x;
			}
			return res;
		}
	};
}

/**************************************/
/*********** END OF NYA LIB ***********/
/**************************************/

using namespace NyaGadget;
//using mll = ModLL< 1000000007 >;
//using mll = ModLL< 998244353 >;

int main(void)
{
	ll N, K; cin >> N >> K;

	if (NT_Counting<ll>::C(N - 1, 2) < K)
	{
		cout << -1;
		return 0;
	}

	vt<pair<ll, ll>> ans;
	rep(i, 2, N+1) ans.push_back({ 1,i });
	
	ll k = NT_Counting<ll>::C(N - 1, 2);
	if (k != K)
	{
		rep(i, 2, N) rep(j, i + 1, N + 1)
		{
			ans.push_back({ i,j });
			k--;
			if (k == K) i = j = loop_end;
		}
	}

	cout << Size(ans) << endl;
	each(i, e, ans) cout << e.f << " " << e.s << endl;
	return 0;
}


Measured memory_bytes: 512