#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
const double eps = 1E-7;
const int maxn = 100005;
struct TData {
  int v, id;
} a[maxn];
int n, p[maxn], w[maxn];
bool us[maxn];
vector<pair<int, int> > li;
inline bool cmpa(TData u, TData v) {
  return u.v < v.v || u.v == v.v && u.id < v.id;
}
inline int chk(int v) {
  if (!v) return 0;
  for (int t = v; t; t /= 10)
    if (t % 10 != 4 && t % 10 != 7) return 0;
  return 1;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) {
    scanf("%d", &a[i].v);
    a[i].id = i;
  }
  sort(a + 1, a + n + 1, cmpa);
  int wh = 0;
  for (int i = 1; i <= n; ++i)
    if (a[i].id != i) wh = 1;
  if (!wh) {
    puts("0");
    return 0;
  }
  wh = 0;
  for (int i = 1; i <= n; ++i) {
    w[i] = chk(a[i].v);
    if (w[i]) wh = a[i].id;
  }
  if (!wh) {
    puts("-1");
    return 0;
  }
  li.clear();
  memset((us), 0, sizeof((us)));
  p[0] = 0;
  for (int j = wh; !us[j]; j = a[j].id) {
    us[j] = 1;
    p[++p[0]] = j;
  }
  for (int j = 1; j < p[0]; ++j) li.push_back(make_pair(p[j], p[j + 1]));
  wh = p[p[0]];
  for (int i = 1; i <= n; ++i)
    if (!us[i]) {
      p[0] = 0;
      for (int j = i; !us[j]; j = a[j].id) {
        us[j] = 1;
        p[++p[0]] = j;
      }
      if (p[0] > 1) {
        li.push_back(make_pair(wh, p[1]));
        for (int j = 1; j < p[0]; ++j) li.push_back(make_pair(p[j], p[j + 1]));
        li.push_back(make_pair(wh, p[p[0]]));
      }
    }
  printf("%d\n", ((int)li.size()));
  for (int i = 0; i < ((int)li.size()); ++i)
    printf("%d %d\n", li[i].first, li[i].second);
  return 0;
}
