#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 20;
int N, wh[maxn], val, pos;
pair<int, int> ar[maxn];
vector<pair<int, int> > v, q;
bool lucky(int a) {
  while (a) {
    if (a % 10 != 4 && a % 10 != 7) return 0;
    a /= 10;
  }
  return 1;
}
int main() {
  scanf("%d", &N);
  for (int i = 1; i <= N; i++) {
    scanf("%d", &ar[i].first);
    ar[i].second = i;
    q.push_back(ar[i]);
    wh[i] = i;
  }
  sort(q.begin(), q.end());
  int flag = 1;
  for (int i = 1; i <= N; i++)
    if (ar[i].first != q[i - 1].first) {
      flag = 0;
      break;
    }
  if (flag) {
    printf("0\n");
    return 0;
  }
  for (int i = 0; i < N; i++)
    if (lucky(q[i].first)) {
      val = q[i].second;
      pos = i + 1;
      break;
    }
  if (!val) {
    printf("-1\n");
    return 0;
  }
  for (int i = 1; i <= N; i++)
    if (i != pos) {
      if (wh[ar[i].second] != wh[val]) {
        v.push_back(pair<int, int>(wh[ar[i].second], wh[val]));
        swap(wh[ar[i].second], wh[val]);
        swap(ar[wh[ar[i].second]], ar[wh[val]]);
      }
      v.push_back(pair<int, int>(wh[q[i - 1].second], wh[val]));
      swap(wh[q[i - 1].second], wh[val]);
      swap(ar[wh[q[i - 1].second]], ar[wh[val]]);
    }
  printf("%d\n", v.size());
  for (int i = 0; i < v.size(); i++) printf("%d %d\n", v[i].first, v[i].second);
  return 0;
}
