#include <bits/stdc++.h>
#define pb push_back
#define loop(i, n) for (int i=0;i<n;i++)
#define lv(i, v) for (int i=0;i<adj[v].size();i++)
#define MAXN INT_MAX
#define F first
#define S second

using namespace std;
const int MAX = 5e5+9;
const int MIN = 1e3+9;
int arr[MAX],A[MAX];
bool vis[MAX],done[MAX];
vector <int> adj[MAX];

void DFS (int v){
	done [v] = 1;
	lv (i, v){
		int u = adj[v][i];
		if (!done[u]){
			DFS (u);
		}
	}
}

int check (int v){
    vis[v] = 1;
	lv (i, v){
		int u = adj[v][i];
		//cout << u << " " << v << " " << arr[u] << endl;
		if (u == v) return u;
		else if (vis[u]) return MAX;
        check (u);
	}
}

int main ()
{
	int n, root = -1, temp , res = 0, t = 1;
	scanf("%d", &n);
	loop (i, n) {
		scanf("%d", &arr[i]);
		arr[i]--;
		A[i] = arr[i];
		if (arr[i] == i) root = i ;
	}
	cout << root << endl ;
	loop (i, n){
			adj[i].pb(arr[i]);
	}
	loop (i,n){
		memset(vis, 0, sizeof(vis));

        temp = check(i);
		cout << temp << " " << check(i) << endl ;

		if (i == root || done [i]) continue ;
		else if (temp == MAX && temp != root){
			A[i] = root;
			DFS (i);
		}
		else {
            A[temp] = root ;
			DFS (i);
		}
	}
	//loop(i, n)
	//	if (arr[i] != A[i]) res++;
	//printf("%d\n",res);
	//loop(i, n)
	//	printf("%d ",A[i]+1);
	return 0;
}