#include "books.h"
#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define mp make_pair
using namespace std;
const int maxn = 1000100;
bool suffix[maxn];
int n, loc[maxn];
long long minimum_walk(std::vector<int> p, int s) {
n = p.size();
suffix[n] = true;
for(int i=n-1;i>=0;i--) {
suffix[i] = suffix[i+1] && (p[i] == i);
loc[p[i]] = i;
}
ll result = 0LL;
set<int>need;
for(int i=0;i<n;i++) {
if(suffix[i+1]) break;
// if p[i] is in need
if(need.find(p[i]) != need.end()) need.erase(p[i]);
if(loc[i] > i) need.insert(i);
/*cout<<"i: \n";
for(int i:need) {
cout<<i<<" ";
} cout<<"\n";*/
result += 2LL * max(1, int(need.size()));
}
return result;
}
