#include <bits/stdc++.h>
using namespace std;
int n, m, k;
bool cover[301];
int linked[301][301];
int MAIN() {
  vector<int> coverSet;
  memset(cover, false, sizeof(cover));
  cin >> n >> m >> k;
  for (int i = 1; i <= k; i++) {
    int node;
    cin >> node;
    cover[node] = true;
    coverSet.push_back(node);
  }
  for (int i = 1; i <= n; i++)
    if (!cover[i]) coverSet.push_back(i);
  if (k == n) {
    cout << "-1" << endl;
  } else {
    int c = 1;
    while (cover[c]) c++;
    int a = 0, b = 0;
    while (coverSet[a] == c) a++;
    while (coverSet[b] == coverSet[a] || coverSet[b] == c) b++;
    a = coverSet[a];
    b = coverSet[b];
    memset(linked, false, sizeof(linked));
    int remain = m;
    linked[a][c] = 1, remain--;
    linked[b][c] = 1, remain--;
    for (int i = 1; i <= n; i++)
      if (i != a && i != b && i != c) {
        linked[i][a] = 1, remain--;
      }
    for (int i = 1; i <= n; i++)
      if (i != a && i != b && i != c) {
        if (remain > 0) linked[i][c] = 1, remain--;
        if (remain > 0 && cover[i] == false) linked[i][b] = 1, remain--;
        for (int j = 1; j < i; j++)
          if (j != a && j != b && j != c)
            if (remain > 0) linked[i][j] = 1, remain--;
      }
    if (remain > 0)
      cout << -1 << endl;
    else {
      for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
          if (linked[i][j]) cout << i << " " << j << endl;
    }
  }
  return 0;
}
int main() {
  ios ::sync_with_stdio(false);
  cout << fixed << setprecision(16);
  return MAIN();
}
