#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define IS_BIT_ON(bit, i) (bit & (1 << i))
#define BIT_ON(bit, i) (bit | (1 << i))
#define BIT_OFF(bit, i) (bit & ~(1 << i))
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
void print() { std::cout << std::endl; }
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) { std::cout << head; if (sizeof...(tail) != 0) {std::cout << " ";} print(std::forward<Tail>(tail)...); }
template <class T> void print(std::vector<T> &v) {for (auto& a : v) { std::cout << a; if (&a != &v.back()) {std::cout << " ";} }std::cout << std::endl;}
template <class T> void print(std::vector<std::vector<T>> &vv) { for (auto& v : vv) { print(v); }}
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

// 2のべき乗数かどうか
bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

// aとbの最大公約数 O(log min(a, b))
long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

// 数列vの最大公約数 O(N log d)
long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

// aとbの最小公倍数 O(log min(a, b))
long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 58u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};  // 右，下
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};    // 右，下，左，上
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

class Edge {
public:
    int no = 0;
    int from = 0;
    int to = 0;
    long long weight = 0;

    Edge(int no, int from, int to, long long weight) : no(no), from(from), to(to), weight(weight) {
    }

};

class Graph {
public:
    const int N;    // ノード数
    int M = 0;      // エッジ数
    std::vector<std::vector<Edge>> graph;
    Graph(int N) : N(N) {
        this->graph.resize(N);
    }

    void add_undirected_edge(int no, const int u, const int v, const long long w) {
        this->graph.at(u).emplace_back(Edge(no, u, v, w));
        this->graph.at(v).emplace_back(Edge(no, v, u, w));
        this->M++;
    }

    std::vector<std::vector<int>> make_matrix_graph() {
        std::vector<std::vector<int>> matrix(this->N, std::vector<int>(this->N, INT_MAX));
        for (const auto &v : this->graph) {
            for (const auto &e : v) {
                matrix[e.from][e.to] = e.weight;
            }
        }
        return matrix;
    }

    // mode 0: undirected edge
    // mode 1: directed edge
    void show(int mode = 0) {
        std::cout << this->M << std::endl;
        for (const auto &v : this->graph) {
            for (const auto &e : v) {
                if (mode == 0) {
                    if (e.from < e.to) {
                        std::cout << e.from +  1 << " " << e.to + 1 << std::endl;
                    }
                }
                else {
                    std::cout << e.from << " " << e.to << std::endl;
                }
            }
        }
    }


};

void solve(LL N, LL K) {
    Graph graph(N);
    FOR(i, 0, N - 1) {
        graph.add_undirected_edge(0, 0, i + 1, 1);
    }

    LL now = ((N - 1) * (N - 2)) / 2;
    if (K > now) {
        print(-1);
        return;
    }

    int target = 1;
    while (now > K) {
        FOR(to, target + 1, N) {
            graph.add_undirected_edge(0, target, to, 1);
            now--;
            if (now <= K) {
                break;
            }
        }
        target++;
    }

    graph.show(0);
}

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

    LL N, K;
    cin >> N >> K;

    solve(N, K);

    return 0;
}



Measured memory_bytes: 640