////////////////////////////////////////////////
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

namespace my {
/*汎用*/
template <typename T>
void input_vec(vector<T> &a, ll n) {
  assert(a.empty());
  for (ll i = 0; i < n; i++) {
    T tmp;
    cin >> tmp;
    a.push_back(tmp);
  }
}
template <typename T>
void input_set(set<T> &a, ll n) {
  assert(a.empty());
  for (ll i = 0; i < n; i++) {
    T tmp;
    cin >> tmp;
    a.insert(tmp);
  }
}

char itoc(int i) { return i + '0'; }
int ctoi(char c) { return c - '0'; }

/*整数*/
ll gcd(ll a, ll b) {  // O( log(max(a,b)) )
  a = abs(a);
  b = abs(b);
  if (a < b) swap(a, b);
  while (b != 0) {
    a %= b;
    swap(a, b);
  }
  return a;
}
ll lcm(ll a, ll b) { return a * (b / my::gcd(a, b)); }  // O( log(max(a,b)) )
ll modinv(ll n, ll mod) {                               // O( log(max(n,mod)) )
  assert(mod > 0 && my::gcd(n, mod) == 1);
  n %= mod;
  if (n < 0) n += mod;
  ll a = mod, b = n, x = 1, y = 0;
  while (b != 0) {
    ll q = a / b, r = a % b;
    a = b;
    b = r;
    y -= q * x;
    swap(x, y);
  }
  y %= mod;
  if (y < 0) y += mod;
  return y;
}

bool is_prime(ll n) {  // O( sqrt(n) )
  bool flag = true;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      flag = false;
      break;
    }
  }
  return flag;
}
vector<pair<ll, ll>> prime_factorize(ll n) {  // O( sqrt(n) )
  vector<pair<ll, ll>> ret;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i != 0) continue;
    ll exp = 0;
    while (n % i == 0) {
      n /= i;
      exp++;
    }
    ret.push_back(make_pair(i, exp));
  }
  if (n != 1) ret.push_back(make_pair(n, 1));
  return ret;
}

/*union find*/
class unionfind {
 private:
  /*根のparの値は「-(その木の要素数)」とする*/
  ll n_;
  vector<ll> par;

  ll root(ll a) {  // O( log(n) )
    if (par.at(a) < 0)
      return a;
    else {
      par.at(a) = root(par.at(a));  //経路圧縮
      return par.at(a);
    }
  }

 public:
  unionfind(ll n) : n_(n), par(n, -1) {}  // O(n)

  void unite(ll a, ll b) {  // O( log(n) )
    assert(0 <= a && a < n_);
    assert(0 <= b && b < n_);
    if (root(a) == root(b))
      return;
    else {
      ll ra = root(a), rb = root(b);
      if (-par.at(ra) < -par.at(rb)) swap(ra, rb);  //サイズによる併合
      par.at(ra) += par.at(rb);
      par.at(rb) = ra;
    }
  }

  bool is_same(ll a, ll b) {  // O( log(n) )
    assert(0 <= a && a < n_);
    assert(0 <= b && b < n_);
    return root(a) == root(b);
  }

  ll size(ll a) {  // O( log(n) )
    assert(0 <= a && a < n_);
    return -par.at(root(a));
  }
};
}  // namespace my
////////////////////////////////////////////////

int main() {
  ll n, m;
  cin >> n >> m;
  if ((m != 0 && m == n - 1) || m == n || m < 0) {
    cout << -1 << endl;
    return 0;
  }

  vector<pair<ll, ll>> lr;
  ll tmpl = 1, tmpr = 2LL * n;
  for (ll i = 0; i < n - m - 1; i++) {
    lr.push_back(make_pair(tmpl, tmpr));
    tmpl++;
    tmpr--;
  }
  for (ll i = tmpl; i + 1 <= tmpr; i += 2) {
    lr.push_back(make_pair(i, i + 1));
  }

  for (auto &lri : lr) cout << lri.first << " " << lri.second << endl;
}
#include<bits/stdc++.h>
#include <iostream>

using namespace std;

int main()
{
    #ifdef LOCAL_EXEC
    #else
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    #endif // LOCAL_EXEC
    long long int n,i,j,k,x=0,y,z,sum=0;
    cin>>n>>k;
    long long int cnt[n+1]={0};
    for(i=1;i<=n;i++){
        cin>>x;
        cnt[x]+=1;
    }
    y=n;
    for(i=1;i<=k;i++){
        for(j=0;j<=n;j++){
            if(cnt[j]==0||y==0)
                break;
            cnt[j]-=1;
            y-=1;
        }
        sum+=j;
        if(y==0)
            break;
    }
    cout<<sum;
    return 0;
}
