#include "books.h"
#include <bits/stdc++.h>
#define debug printf
#define lp(i,a,b) for(int i = a ; i < b; i++)
#define pb push_back
#define ff first
#define ss second
#define mk make_pair
#define pii pair<int,int>
#define ll long long
#define all(x) x.begin(),x.end()
#define sz(x) (int)(x.size())
using namespace std ;
long long minimum_walk(vector<int> p, int S)
{
assert( S == 0 ) ;
int n = sz(p) ;
long long ans = 0 ;
int l , r ;
for(l = 0 ; l < n ; l++ )
{
if(p[l] == l) ans += 2LL ;
else break ;
}
if(l == n) return 0 ;
for(r = n-1 ; r>= 0 ; r-- )
if( p[r] != r ) break ;
set<int> s ;
s.insert( p[l] ) ;
for(int i = l+1 ; i <= r ; i++ )
{
while( sz(s) )
{
auto it = s.begin() ;
if( *it <= i-1 ) s.erase(it) ;
else break ;
}
//Sobre a aresta i-1 -> i
ans += max(2LL, 2LL*sz(s) ) ;
s.insert( p[i] ) ;
}
return ans ;
}
