Gym 100971B Water & Fool

Description

Standard Input/output
Announcement

• Statements
  

  A permutation of n numbers is a sequence of the integers from 1 to n where all number is occurred E Xactly once. If a permutation p_{1, P2, ..., pn have an index i su Ch that pi = i, this index is called a fixed point.}

  A derangement is a permutation without any fixed points.

  Let's denote the operation swap(a, b) as swapping elements on positions a and b.

  For the given permutation find the minimal number of swaps operations needed to turn it into derangement.

Input

The first line contains an integer n(2≤ n ≤200000)-the number of elements in a Permuta tion.

The second line contains the elements of the permutation- n distinct integers from 1 to n .

Output

In the first line output a single integer k -the minimal number of swaps operations needed to TR Ansform the permutation into derangement.

In each of the next k lines output integers a_{i and bI (1≤ ai, bi ≤ n)-the arguments of C23>swap operations.}

If There is multiple possible solutions, output any of them.

Sample Input

Input

6
6 2 4 3 5 1

Output

1
2 5

Test instructions: Make I! =pi  moves the fewest number of times  and outputs the position of both of the interchanges

The puzzle: Find the so-called position to be exchanged if the number is even, then direct 22 exchange
     
     When the first position is given, pay attention to the special sentence.

1#include <bits/stdc++.h>2 using namespacestd;3 intN;4 inta[200005];5 //int where[200005];6 intaa[200005];7 intMain ()8 {9scanf"%d",&n);Ten      for(intI=1; i<=n;i++) One         { Ascanf"%d",&a[i]); -             //where[a[i]]=i; -         } the     intans=0; -      for(intI=1; i<=n;i++) -     { -         if(a[i]==i) +         { -ans++; +aa[ans]=i; A         } at     } -     if(ans%2==0) -     { -cout<<ans/2<<Endl; -          for(intI=1; i<ans;i+=2) -cout<<aa[i]<<" "<<aa[i+1]<<Endl; in     } -     Else to     { +cout<<ans/2+1<<Endl; -          for(intI=1; i<ans;i+=2) thecout<<aa[i]<<" "<<aa[i+1]<<Endl; *         if(aa[ans]==1) $cout<<"1 2"<<Endl;Panax Notoginseng         Else -cout<<aa[ans]-1<<" "<<aa[ans]<<Endl; the     } +     return 0; A}

#include <bits/stdc++.h>
using namespaceStd;
intN;
intA[200005];
//int where[200005];
intAa[200005];
int Main()
{
scanf("%d",&N);
for(intI=1;I<=N;I++)
{
scanf("%d",&A[I]);
//where[a[i]]=i;
}
intAns=0;
for(intI=1;I<=N;I++)
{
if(A[I]==I)
{
Ans++;
Aa[Ans]=I;
}
}
if(Ans%2==0)
{
cout<<Ans/2<<Endl;
for(intI=1;I<Ans;I+=2)
cout<<Aa[I]<<" "<<Aa[I+1]<<Endl;
}
Else
{
cout<<Ans/2+1<<Endl;
for(intI=1;I<Ans;I+=2)
cout<<Aa[I]<<" "<<Aa[I+1]<<Endl;
if(Aa[Ans]==1)
cout<<"1 2"<<Endl;
Else
cout<<Aa[Ans]-1<<" "<<Aa[Ans]<<Endl;
}
return 0;
}

Gym 100971B Water & Fool