#include <bits/stdc++.h>
using namespace std;
template <class T>
bool uin(T &a, T b) {
  return a > b ? (a = b, true) : false;
}
template <class T>
bool uax(T &a, T b) {
  return a < b ? (a = b, true) : false;
}
const int N = (int)1e5 + 100;
int tc, n, pos[N], nowp[N];
vector<pair<int, int> > a, b, ans;
bool chk(int num) {
  while (num > 0) {
    if (num % 10 != 4 && num % 10 != 7) return false;
    num /= 10;
  }
  return true;
}
void gao(int &l, int &r) {
  if (l != r) ans.emplace_back(make_pair(l, r));
  swap(b[l], b[r]);
  swap(l, r);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.precision(10);
  cout << fixed;
  cin >> n;
  bool found = false;
  int p = -1;
  a.emplace_back(make_pair(-1, -1)), b.emplace_back(make_pair(-1, -1));
  for (int i = 1; i <= (int)(n); ++i) {
    int x;
    cin >> x;
    found |= chk(x);
    if (chk(x)) p = i;
    a.emplace_back(make_pair(x, i));
    b.emplace_back(make_pair(x, i));
  }
  if (!found) {
    bool ok = true;
    for (int i = 2; i <= n; ++i) ok &= (b[i].first >= b[i - 1].first);
    cout << (ok ? 0 : -1) << '\n';
    return 0;
  }
  sort((a).begin(), (a).end());
  for (int i = 1; i <= (int)(n); ++i) {
    pos[i] = a[i].second;
    nowp[i] = i;
  }
  for (int i = 1; i <= (int)(n); ++i) {
    if (pos[i] == b[i].second) continue;
    gao(nowp[b[i].second], nowp[p]);
    gao(nowp[p], nowp[pos[i]]);
  }
  cout << int(ans.size()) << '\n';
  for (pair<int, int> now : ans) cout << now.first << ' ' << now.second << '\n';
  return 0;
}
