CF432C.Prime Swaps

You have an array $a[1],a[2],...,a[n]$ , containing distinct integers from $1$ to $n$ . Your task is to sort this array in increasing order with the following operation (you may need to apply it multiple times):

• choose two indexes, $i$ and $j$ ( 1<=i<j<=n ; $(j-i+1)$ is a prime number);
• swap the elements on positions $i$ and $j$ ; in other words, you are allowed to apply the following sequence of assignments: $tmp=a[i],a[i]=a[j],a[j]=tmp$ ( $tmp$ is a temporary variable).

You do not need to minimize the number of used operations. However, you need to make sure that there are at most $5n$ operations.

The first line contains integer $n$ $(1<=n<=10^{5})$ . The next line contains $n$ distinct integers $a[1],a[2],...,a[n]$ $(1<=a[i]<=n)$ .

In the first line, print integer $k$ $(0<=k<=5n)$ — the number of used operations. Next, print the operations. Each operation must be printed as " $i$ $j$ " ( 1<=i<j<=n ; $(j-i+1)$ is a prime).

If there are multiple answers, you can print any of them.