Problem: Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Petya got an array consisting of n numbers, it is the gift for his birthday. Now he wants to sort it in the non-decreasing order. However, a usual sorting is boring to perform, that's why Petya invented the following limitation: one can swap any two numbers but only if at least one of them is lucky. Your task is to sort the array according to the specified limitation. Find any possible sequence of the swaps (the number of operations in the sequence should not exceed 2n).

Input

The first line contains an integer n (1 ≤ n ≤ 105) — the number of elements in the array. The second line contains n positive integers, not exceeding 109 — the array that needs to be sorted in the non-decreasing order.

Output

On the first line print number k (0 ≤ k ≤ 2n) — the number of the swaps in the sorting. On the following k lines print one pair of distinct numbers (a pair per line) — the indexes of elements to swap. The numbers in the array are numbered starting from 1. If it is impossible to sort the given sequence, print the single number -1.

If there are several solutions, output any. Note that you don't have to minimize k. Any sorting with no more than 2n swaps is accepted.

Examples

Input

2
4 7


Output

0


Input

3
4 2 1


Output

1
1 3


Input

7
77 66 55 44 33 22 11


Output

7
1 7
7 2
2 6
6 7
3 4
5 3
4 5

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
enum Color { RED = 0, BLACK = 1 };
template <class T1, class T2>
struct RedBlackTree {
  RedBlackTree()
      : parent(NULL), left(NULL), right(NULL), color(BLACK), key(0), value(0){};
  RedBlackTree(T1 _key, T2 _value)
      : parent(NULL),
        left(NULL),
        right(NULL),
        color(BLACK),
        key(_key),
        value(_value){};
  T1 key;
  T2 value;
  Color color;
  RedBlackTree *parent, *left, *right;
  RedBlackTree* operator=(const T2& _value) {
    value = _value;
    return this;
  };
};
template <class T1, class T2>
void CopyData(RedBlackTree<T1, T2>*& z, RedBlackTree<T1, T2>*& y) {
  z->value = y->value;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Find(RedBlackTree<T1, T2>* x, T1 k) {
  while (x != NULL && k != x->key) {
    if (k < x->key)
      x = x->left;
    else
      x = x->right;
  }
  return x;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Minimum(RedBlackTree<T1, T2>* root) {
  if (root == NULL) return NULL;
  while (root->left != NULL) root = root->left;
  return root;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Maximum(RedBlackTree<T1, T2>* root) {
  if (root == NULL) return NULL;
  while (root->right != NULL) root = root->right;
  return root;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Successor(RedBlackTree<T1, T2>* root) {
  if (root == NULL) return NULL;
  if (root->right != NULL) return Minimum(root->right);
  RedBlackTree<T1, T2>* y = root->parent;
  while (y != NULL && root == y->right) {
    root = y;
    y = y->parent;
  }
  return y;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Predecessor(RedBlackTree<T1, T2>* root) {
  if (root == NULL) return NULL;
  if (root->left != NULL) return Maximum(root->left);
  RedBlackTree<T1, T2>* y = root->parent;
  while (y != NULL && root == y->left) {
    root = y;
    y = y->parent;
  }
  return y;
}
template <class T1, class T2>
void LeftRotate(RedBlackTree<T1, T2>*& root, RedBlackTree<T1, T2>* x) {
  if (x->right == NULL) return;
  RedBlackTree<T1, T2>* y = x->right;
  x->right = y->left;
  if (y->left != NULL) y->left->parent = x;
  y->parent = x->parent;
  if (x->parent == NULL)
    root = y;
  else {
    if (x == x->parent->left)
      x->parent->left = y;
    else
      x->parent->right = y;
  }
  y->left = x;
  x->parent = y;
}
template <class T1, class T2>
void RightRotate(RedBlackTree<T1, T2>*& root, RedBlackTree<T1, T2>* y) {
  if (y->left == NULL) return;
  RedBlackTree<T1, T2>* x = y->left;
  y->left = x->right;
  if (x->right != NULL) x->right->parent = y;
  x->parent = y->parent;
  if (y->parent == NULL)
    root = x;
  else {
    if (y == y->parent->left)
      y->parent->left = x;
    else
      y->parent->right = x;
  }
  x->right = y;
  y->parent = x;
}
template <class T1, class T2>
void InsertFixup(RedBlackTree<T1, T2>*& root, RedBlackTree<T1, T2>* z) {
  while (z->parent != NULL && z->parent->color == RED) {
    if (z->parent == z->parent->parent->left) {
      RedBlackTree<T1, T2>* y = z->parent->parent->right;
      if (y != NULL && y->color == RED) {
        z->parent->color = BLACK;
        y->color = BLACK;
        z->parent->parent->color = RED;
        z = z->parent->parent;
      } else {
        if (z == z->parent->right) {
          z = z->parent;
          LeftRotate(root, z);
        }
        z->parent->color = BLACK;
        z->parent->parent->color = RED;
        RightRotate(root, z->parent->parent);
      }
    } else {
      RedBlackTree<T1, T2>* y = z->parent->parent->left;
      if (y != NULL && y->color == RED) {
        z->parent->color = BLACK;
        y->color = BLACK;
        z->parent->parent->color = RED;
        z = z->parent->parent;
      } else {
        if (z == z->parent->left) {
          z = z->parent;
          RightRotate(root, z);
        }
        z->parent->color = BLACK;
        z->parent->parent->color = RED;
        LeftRotate(root, z->parent->parent);
      }
    }
  }
  root->color = BLACK;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Insert(RedBlackTree<T1, T2>*& root, T1 key, T2 value) {
  RedBlackTree<T1, T2>* z = new RedBlackTree<T1, T2>(key, value);
  RedBlackTree<T1, T2>*y = NULL, *x = root;
  while (x != NULL) {
    y = x;
    if (z->key < x->key)
      x = x->left;
    else
      x = x->right;
  }
  z->parent = y;
  if (y == NULL)
    root = z;
  else {
    if (z->key < y->key)
      y->left = z;
    else
      y->right = z;
  }
  z->left = NULL;
  z->right = NULL;
  z->color = RED;
  InsertFixup(root, z);
  return z;
}
template <class T1, class T2>
void DeleteFixup(RedBlackTree<T1, T2>*& root, RedBlackTree<T1, T2>* x) {
  while (x != NULL && x != root && x->color == BLACK) {
    if (x == x->parent->left) {
      RedBlackTree<T1, T2>* w = x->parent->right;
      if (w != NULL && w->color == RED) {
        w->color = BLACK;
        x->parent->color = RED;
        LeftRotate(root, x->parent);
        w = x->parent->right;
      }
      if (w->left->color == BLACK && w->right->color == BLACK) {
        w->color = RED;
        x = x->parent;
      } else {
        if (w->right->color == BLACK) {
          w->left->color = BLACK;
          w->color = RED;
          RightRotate(root, w);
          w = x->parent->right;
        }
        w->color = x->parent->color;
        x->parent->color = BLACK;
        w->right->color = BLACK;
        LeftRotate(root, x->parent);
        x = root;
      }
    } else {
      RedBlackTree<T1, T2>* w = x->parent->left;
      if (w != NULL && w->color == RED) {
        w->color = BLACK;
        x->parent->color = RED;
        RightRotate(root, x->parent);
        w = x->parent->left;
      }
      if (w->left->color == BLACK && w->right->color == BLACK) {
        w->color = RED;
        x = x->parent;
      } else {
        if (w->left->color == BLACK) {
          w->right->color = BLACK;
          w->color = RED;
          LeftRotate(root, w);
          w = x->parent->left;
        }
        w->color = x->parent->color;
        x->parent->color = BLACK;
        w->left->color = BLACK;
        RightRotate(root, x->parent);
        x = root;
      }
    }
  }
  if (x != NULL) x->color = BLACK;
}
template <class T1, class T2>
RedBlackTree<T1, T2>* Delete(RedBlackTree<T1, T2>*& root,
                             RedBlackTree<T1, T2>* z) {
  RedBlackTree<T1, T2>*y, *x;
  if (z->left == NULL || z->right == NULL)
    y = z;
  else
    y = Successor(z);
  if (y->left != NULL)
    x = y->left;
  else
    x = y->right;
  if (x != NULL) x->parent = y->parent;
  if (y->parent == NULL)
    root = x;
  else if (y == y->parent->left)
    y->parent->left = x;
  else
    y->parent->right = x;
  if (y != z) {
    z->key = y->key;
    CopyData(z, y);
  }
  if (y->color == BLACK) DeleteFixup(root, x);
  return y;
}
template <class T1, class T2>
void Clear(RedBlackTree<T1, T2>*& root) {
  if (root == NULL) return;
  Clear(root->left);
  Clear(root->right);
  delete root;
  root = NULL;
}
template <class T1, class T2>
void Output(RedBlackTree<T1, T2>* root, int cnt = 0) {
  if (root == NULL) return;
  Output(root->right, cnt + 1);
  for (int i = 0; i < cnt; ++i) cout << "   ";
  cout << "(" << root->key << ";" << root->color << ";" << root->value << ")\n";
  Output(root->left, cnt + 1);
}
template <class T1, class T2>
struct myMap {
  myMap() : root(NULL){};
  RedBlackTree<T1, T2>* root;
  RedBlackTree<T1, T2>* count(const T1& key);
  T2& operator[](const T1& key);
  void clear() { Clear(root); };
  RedBlackTree<T1, T2>* insert(const pair<T1, T2>& value);
  RedBlackTree<T1, T2>* begin();
  RedBlackTree<T1, T2>* end() { return Maximum(root); };
  struct iterator {
    iterator() : node(NULL){};
    iterator(RedBlackTree<T1, T2>* _node) : node(_node){};
    RedBlackTree<T1, T2>* node;
    iterator& operator++() {
      node = Successor(node);
      return *this;
    }
    iterator operator++(int) {
      RedBlackTree<T1, T2>* tmp = node;
      node = Successor(node);
      return tmp;
    }
    iterator& operator--() {
      node = Predecessor(node);
      return *this;
    }
    iterator operator--(int) {
      RedBlackTree<T1, T2>* tmp = node;
      node = Predecessor(node);
      return tmp;
    }
    bool operator!=(const iterator& it) { return it.node != node; }
    RedBlackTree<T1, T2>*& operator->() { return node; }
  };
};
template <class T1, class T2>
RedBlackTree<T1, T2>* myMap<T1, T2>::begin() {
  return Minimum(root);
}
template <class T1, class T2>
RedBlackTree<T1, T2>* myMap<T1, T2>::count(const T1& key) {
  return Find(root, key);
}
template <class T1, class T2>
RedBlackTree<T1, T2>* myMap<T1, T2>::insert(const pair<T1, T2>& value) {
  return Insert(root, value.first, value.second);
}
template <class T1, class T2>
T2& myMap<T1, T2>::operator[](const T1& key) {
  RedBlackTree<T1, T2>* ret = count(key);
  if (ret == NULL) ret = Insert(root, key, T2());
  return ret->value;
}
int nums[100005], n, v[100005], A[100005];
myMap<int, int> f, s;
bool isOk(int a) {
  if (a == 0) return false;
  while (a) {
    if (a % 10 != 4 && a % 10 != 7) return false;
    a /= 10;
  }
  return true;
}
vector<int> x, y;
pair<int, int> vv[100005];
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d", &nums[i]);
    A[i] = v[i] = nums[i];
    vv[i] = make_pair(nums[i], i);
  }
  sort(v, v + n);
  int pos = -1, happy;
  for (int i = 0; i < n; i++) {
    if (isOk(nums[i])) {
      pos = i;
      happy = nums[i];
      break;
    }
  }
  if (pos != -1) {
    sort(vv, vv + n);
    for (int i = 0; i < n; i++) nums[vv[i].second] = i + 1;
    for (int i = 0; i < n; i++) {
      v[i] = nums[i];
      f[v[i]] = i;
    }
    happy = v[pos];
    sort(v, v + n);
    for (int i = 0; i < n; i++) s[i] = v[i];
    for (int i = 0; i < n; i++) {
      int a = f[happy], b = i, pa = a, pb = b;
      if (a != b) {
        swap(nums[a], nums[b]);
        swap(A[a], A[b]);
        x.push_back(a);
        y.push_back(b);
        f[nums[a]] = a;
        f[nums[b]] = b;
      }
      a = f[happy], b = f[s[i]];
      if (a != b) {
        swap(nums[a], nums[b]);
        swap(A[a], A[b]);
        x.push_back(a);
        y.push_back(b);
        f[nums[a]] = a;
        f[nums[b]] = b;
      }
      if (pa != pb && min(pa, pb) == min(a, b) && max(pa, pb) == max(a, b)) {
        x.pop_back();
        y.pop_back();
        x.pop_back();
        y.pop_back();
      }
    }
    printf("%d\n", x.size());
    for (int i = 0; i < x.size(); i++) printf("%d %d\n", x[i] + 1, y[i] + 1);
  } else {
    for (int i = 1; i < n; i++)
      if (A[i - 1] > A[i]) {
        cout << -1 << endl;
        return 0;
      }
    cout << 0 << endl;
  }
  return 0;
}