#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:500000000")
using namespace std;
int ans[305][305], d[305][305];
int a[305];
int n, k;
bool used[305];
bool h[305][305];
void G() {
  for (int i = 1; i <= k; i++) {
    int v = a[i];
    for (int j = 1; j <= n; j++)
      for (int r = 1; r <= n; r++)
        ans[j][r] = min(ans[j][r], ans[j][v] + ans[v][r]);
  }
}
void F() {
  for (int k = 1; k <= n; k++)
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= n; j++) d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}
int main() {
  int m, i, j;
  cin >> n >> m >> k;
  for (i = 1; i <= k; i++) scanf("%d", &a[i]), used[a[i]] = true;
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= n; j++) {
      if (i == j)
        ans[i][j] = 0;
      else
        ans[i][j] = 0x3f3f3f3f;
      d[i][j] = ans[i][j];
    }
  }
  for (i = 1; m > 0 && i <= n; i++)
    if (!used[i]) {
      for (j = 1; m > 0 && j <= n; j++)
        if (j != i && !h[i][j]) {
          h[i][j] = h[j][i] = true;
          ans[i][j] = ans[j][i] = d[i][j] = d[j][i] = 1;
          m--;
        }
    }
  while (m > 0) {
    for (i = 1; i <= n; i++)
      for (j = 1; j < i; j++)
        if (!h[i][j] && m > 0) {
          h[i][j] = h[j][i] = true;
          ans[i][j] = ans[j][i] = d[i][j] = d[j][i] = 1;
          m--;
        }
  }
  G();
  F();
  bool ok = false;
  for (i = 1; i <= n; i++)
    for (j = 1; j <= n; j++) {
      if (d[i][j] != ans[i][j]) {
        ok = true;
      }
    }
  if (!ok) {
    puts("-1");
  } else {
    for (i = 1; i <= n; i++)
      for (j = 1; j < i; j++)
        if (h[i][j]) printf("%d %d\n", i, j);
  }
}
