#include <bits/stdc++.h>
using namespace std;
int A[310], B[310];
bool v[310];
int N, M, K;
int main() {
  memset(v, 0, sizeof(v));
  scanf("%d%d%d", &N, &M, &K);
  for (int i = 0; i < K; i++) {
    scanf("%d", &A[i]);
    v[A[i]] = 1;
  }
  int y = A[K - 1];
  int x = K - 1;
  int numOfEdge = (N * N - N - 2 * K + 2) / 2;
  if (M > numOfEdge || K == N) {
    printf("-1\n");
    return 0;
  }
  int m = 0;
  for (int i = 1; i <= N; i++) {
    if (!v[i]) {
      B[m++] = i;
    }
  }
  int cnt = 0;
  for (int i = 1; i < x; i++) {
    printf("%d %d\n", A[i - 1], A[i]);
    cnt++;
  }
  printf("%d %d\n", A[x - 1], B[0]);
  cnt++;
  for (int i = 1; i < m; i++) {
    printf("%d %d\n", B[i - 1], B[i]);
    cnt++;
  }
  printf("%d %d\n", B[m - 1], y);
  cnt++;
  if (cnt == M) return 0;
  for (int i = 0; i < m; i++) {
    A[x++] = B[i];
  }
  for (int i = 0; i < x; i++) {
    if (cnt == M) break;
    for (int j = i + 2; j < x; j++) {
      if (cnt == M) break;
      printf("%d %d\n", A[i], A[j]);
      cnt++;
    }
  }
  for (int i = 0; i < m - 1; i++) {
    if (cnt == M) break;
    printf("%d %d\n", B[i], y);
    cnt++;
  }
  return 0;
}
