#include <bits/stdc++.h>
using namespace std;
const int N = 101010;
int n, p;
int b[N], c[N], in[N];
pair<int, int> a[N];
vector<pair<int, int> > ans;
bool check(int x) {
  while (x) {
    int t = x % 10;
    if (t != 4 && t != 7) return 0;
    x /= 10;
  }
  return 1;
}
void change(int &x, int y) {
  if (x == y) return;
  ans.push_back(make_pair(x, y));
  swap(c[x], c[y]);
  swap(in[x], in[y]);
  b[in[x]] = x;
  b[in[y]] = y;
  x = y;
}
bool solve() {
  bool ok = 1;
  for (int i = (1); i < (n + 1); i++)
    if (b[i] != i) ok = 0;
  if (ok) return 1;
  if (!p) return 0;
  for (int i = (1); i < (n + 1); i++)
    if (b[i] != i) {
      if (b[i] == p) continue;
      change(p, i);
      change(p, b[i]);
    }
  return 1;
}
int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);
  cin >> n;
  p = 0;
  for (int i = (1); i < (n + 1); i++) {
    cin >> a[i].first, a[i].second = i;
    c[i] = a[i].first;
    if (check(c[i])) p = i;
  }
  sort(a + 1, a + 1 + n);
  for (int i = (1); i < (n + 1); i++) b[i] = a[i].second, in[a[i].second] = i;
  if (solve()) {
    cout << (int)ans.size() << "\n";
    for (int i = (0); i < ((int)ans.size()); i++)
      cout << ans[i].first << " " << ans[i].second << "\n";
  } else {
    cout << "-1"
         << "\n";
  }
  return 0;
}
