#include <bits/stdc++.h>
using namespace std;
#define ln '\n'
#define ll long long
#define pii pair<int, int>
#define pil pair<int, ll>
#define pll pair<ll, ll>
#define all(x) begin(x), end(x)
#define pb emplace_back
#define dump(a) while(a.size())a.pop();
#define p(x) cout << #x << " = " << x << '\n';
#define p2(x) cout << #x << " = {" << x.first << ',' << x.second << "}\n";
#define pv(a) cout << #a << " = "; for(auto _x : a) cout << _x << ' '; cout << '\n';
#define pv2(a) cout << #a << " = "; for(auto [_x,_y] : a)cout << '{' << _x << ',' << _y << "} "; cout << '\n';
#define pa(a,n) cout << #a << " = "; for(int _i = 1; _i <= n; ++_i)cout << a[_i] << ' '; cout << '\n';
#define pa0(a,n) cout << #a << " = "; for(int _i = 0; _i < n; ++_i)cout << a[_i] << ' '; cout << '\n';
#define INF 2e9
#define LINF 2e18
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int uid(int a, int b) { return uniform_int_distribution<int>(a,b)(rng);}
ll uld(ll a, ll b) { return uniform_int_distribution<ll>(a,b)(rng); }
const int N = 5e3 + 3;
void solve() {
int n; cin >> n;
vector<int> v(n), rev(n + 1);
for(int i=0; i<n; ++i) {
cin >> v[i]; rev[v[i]] = i;
}
// pv(v);
// pa(rev, n);
int res = INT_MAX;
vector<int> t(n); iota(all(t), 1);
do {
bool ok = true;
vector<int> pos(n + 1);
for(int i=0; i<n; ++i) {
if(i and t[i-1] >= t[i] + 2) ok = false;
pos[t[i]] = i;
}
if(!ok or t == v) continue ;
// pv(t);
// pa(pos, n);
int mv = 0;
for(int i=0; i<n; ++i) {
for(int j=i+1; j<n; ++j) {
mv += ((pos[v[i]] < pos[v[j]]) != (rev[v[i]] < rev[v[j]]));
}
}
res = min(res, mv);
}while(next_permutation(all(t)));
cout << res ;
}
int32_t main() {
cin.tie(nullptr)->sync_with_stdio(0);
int TC = 1;
// cin >> TC;
while(TC--) solve();
return 0;
}
