#include <bits/stdc++.h>
using namespace std;
int n, m, k, i, x, v1, v2, v;
int u[1000];
int o[1000];
int main() {
  cin >> n >> m >> k;
  for (int i = 0; i < k; i++) {
    cin >> x;
    u[x] = 1;
    if (i == 0) v1 = x;
    if (i == 1) v2 = x;
  }
  if (n == k) {
    cout << -1 << endl;
    return 0;
  }
  v = 1;
  while (u[v]) v++;
  o[0] = v1;
  o[1] = v;
  o[2] = v2;
  int sz = 3;
  for (int i = 1; i <= n; i++)
    if ((i != v) && (i != v1) && (i != v2)) {
      o[sz] = i;
      sz++;
    }
  if ((n - 3) * (n - 3 - 1) / 2 + n - 3 + n - 2 + n - k < m) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < n - 1; i++) cout << o[i] << " " << o[i + 1] << endl;
  m -= (n - 1);
  for (int i = 1; i < n; i++)
    for (int j = i + 2; j < n; j++)
      if (m) {
        cout << o[i] << " " << o[j] << endl;
        m--;
      }
  for (int i = 2; i < n; i++)
    if (m)
      if (!u[o[i]]) {
        cout << o[0] << " " << o[i] << endl;
        m--;
      }
  return 0;
}
