#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int n, a[100005], sta[100005];
vector<int> V;
int calc(int k) {
  while (k) {
    int d = k % 10;
    k /= 10;
    if (d != 4 && d != 7) return 0;
  }
  return 1;
}
using pii = pair<int, int>;
int tar[100005], to[100005];
vector<pii> Ans;
void Swap(int first, int second) {
  if (first == second) return;
  to[tar[first]] = second, to[tar[second]] = first;
  swap(tar[second], tar[first]);
  Ans.push_back(pii(first, second));
  return;
}
int main() {
  V.resize(1100800);
  for (auto first : V) first = rand();
  scanf("%d", &n);
  int g = 0, pos = -1;
  vector<pii> vec;
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sta[i] = calc(a[i]);
    g += sta[i];
    if (sta[i]) pos = i;
    vec.push_back(pii(a[i], i));
  }
  sort(vec.begin(), vec.end());
  for (int i = 0; i < vec.size(); i++) {
    tar[vec[i].second] = i + 1;
    to[i + 1] = vec[i].second;
  }
  if (g == 0) {
    bool flag = 0;
    for (int i = 1; i < n; i++)
      if (a[i] > a[i + 1]) flag = 1;
    if (flag)
      puts("-1");
    else
      puts("0");
  } else {
    assert(pos > 0);
    for (int i = 1; i <= n; i++) {
      Swap(pos, i);
      pos = i;
      int prv = to[i];
      Swap(pos, to[i]);
      pos = prv;
    }
    int sz = Ans.size();
    printf("%d\n", sz);
    for (auto first : Ans) {
      printf("%d %d\n", first.first, first.second);
    }
  }
  return 0;
}
