#include <bits/stdc++.h>
using namespace std;
int BIT(int i, long long x) { return (x & (1 << i)); }
long long ONBIT(int i, long long x) { return (x | (1 << i)); }
long long OFFBIT(int i, long long x) { return (x & ~(1 << i)); }
long long FLIPBIT(int i, long long x) { return (x ^ (1 << i)); }
long long NUMBIT(long long x) { return __builtin_popcount(x); }
template <class T>
T gcd(T a, T b) {
  T r;
  int dem = 0;
  while (b != 0) {
    r = a % b;
    dem++;
    a = b;
    b = r;
  }
  cout << dem << endl;
  return a;
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
const int maxv = 500;
const int maxe = maxv * maxv;
const int inf = (int)1e9 + 5;
const long long linf = (long long)1e16 + 5;
const int dr[] = {-1, 0, +1, 0};
const int dc[] = {0, +1, 0, -1};
const char IN[] = "_.in";
const char OUT[] = "_.out";
const int maxn = 111111;
const int base = 1e9 + 7;
int test;
int n;
int ke[maxn];
bool tham[maxn], in[maxn];
vector<int> come, go;
int dfs(int u) {
  if (tham[u]) return u;
  tham[u] = true;
  return (dfs(ke[u]));
}
int main() {
  cin >> n;
  for (int i = (1); i <= (n); i++) {
    int x;
    cin >> x;
    ke[i] = x;
    in[x] = true;
  }
  for (int i = (1); i <= (n); i++)
    if (!in[i]) {
      come.push_back(i);
      go.push_back(dfs(i));
    }
  for (int i = (1); i <= (n); i++)
    if (!tham[i]) {
      come.push_back(i);
      go.push_back(i);
      dfs(i);
    }
  if (come.size() == 1 && come[0] == go[0])
    cout << 0;
  else {
    cout << come.size() << endl;
    for (int i = (0); i <= (come.size() - 1); i++)
      cout << go[i] << " " << come[(i + 1) % come.size()] << endl;
  }
}
