#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
#include <stack>
#include <sstream>
#include <utility>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <tuple>
#include <array>
#include <bitset>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

bool dp[501][501];
int pre[501][501];

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,k; cin >> n >> k;
    if(n == 1){
        if(k == 0){
            cout << -1 << "\n";
        }
        else{
            cout << 1 << "\n";
            cout << 1 << " " << 1 << "\n";
        }
        return 0;
    }
    dp[0][0] = true;
    for(int i=0;i<n;i++){
        for(int j=0;j<=i;j++){
            if(!dp[i][j]) continue;
            dp[i+1][j] = true;
            pre[i+1][j] = 1;
            if(i+2 <= n){
                dp[i+2][j+1] = true;
                pre[i+2][j+1] = 2;
            }
            // if(i+3 <= n){
            //     dp[i+3][j+2] = true;
            //     pre[i+3][j+2] = 3;
            // }
        }
    }
    if(!dp[n][n-k]){
        cout << -1 << "\n";
        return 0;
    }
    vector<int> v;
    int u = n, uu = n-k;
    while(u){
        int p = pre[u][uu];
        v.push_back(p);
        u -= p;
        uu -= p-1;
    }
    vector<pair<int,int>> res;
    n = 1;
    for(int i:v){
        if(i == 1){
            res.push_back({n,n});
            n++;
        }
        else if(i == 2){
            res.push_back({n,n+1});
            res.push_back({n,n});
            res.push_back({n+1,n+1});
            n += 2;
        }
        // else{
        //     res.push_back({n+1,n+1});
        //     res.push_back({})
        // }
    }
    cout << res.size() << "\n";
    for(auto &p:res){
        cout << p.first << " " << p.second << "\n";
    }
}