#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T l, T r) { while (l != r) cerr << *l << " \n"[next(l)==r], ++l; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
// My bug list :
// integer overflow
// 0based, 1based forgotten
// index out of bound
// n, m, i, j typo
// some cases are missing
const int MAX_N = 310;
int n, p[MAX_N];
int dp[MAX_N][MAX_N][MAX_N];
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0);
cin >> n;
if (n > 300) return 0;
for (int i = 1;i <= n;++i)
cin >> p[i];
int res = 0;
for (int l = 0;l <= n;++l)
for (int r = n+1;r > l+1;--r) {
int sz = l + n - r + 1;
//DE(l, r, sz);
for (int i = 0, lidx = 0, ridx = n - sz + 1;i <= sz;++i, ++lidx, ++ridx) {
//DE(lidx, ridx);
chmax(dp[l+1][r][i+1], dp[l][r][i] + (p[lidx+1] == l+1));
chmax(dp[l+1][r][i], dp[l][r][i] + (p[ridx-1] == l+1));
chmax(dp[l][r-1][i+1], dp[l][r][i] + (p[lidx+1] == r-1));
chmax(dp[l][r-1][i], dp[l][r][i] + (p[ridx-1] == r-1));
}
}
//DE(l, r, sz);
// for (int i = 0;i <= sz;++i) {
// int j = sz - i;
// int mn = i + 1, mx = n - j;
// chmax(dp[l+1][r][i+1], dp[l][r][i] + (p[l+1] == mn));
// chmax(dp[l+1][r][i], dp[l][r][i] + (p[l+1] == mx));
// chmax(dp[l][r-1][i+1], dp[l][r][i] + (p[r-1] == mn));
// chmax(dp[l][r-1][i], dp[l][r][i] + (p[r-1] == mx));
// }
for (int i = 0;i <= n;++i)
for (int j = 0;j <= n;++j)
chmax(res, dp[i][i+1][j]);
cout << n - res << '\n';
}
