F

#include <bits/stdc++.h>


using namespace std;

//#define int long long

const long long INF = 1e9 + 7;
const int MAXN = 1e2 + 10;
const int N = 1e5 + 10;

int dp[MAXN][MAXN], can[MAXN][MAXN];

void solve() {
    int n;
    cin >> n;
    vector<int> a(n + 1);
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
    }
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= n; ++j) {
            dp[i][j] = INF;
            if (i == j) {
                dp[i][j] = 0;
                can[i][j] = 1;
            }
        }
    }
    for (int len = 2; len <= n + 1; ++len) {
        for (int l = 1; l + len - 1 < n + 1; ++l) {
            int r = l + len - 1;
            for (int m = l; m < r; ++m) {
                if (can[l][m] > 0 && can[m][r] > 0 && (a[m] > a[l] && a[m] > a[r] || a[m] < a[l] && a[m] < a[r])) {
                    can[l][r] = m;
                }
            }
            if (a[l] > a[r]) {
                dp[l][r] = INF;
            }
            if (can[l][r]) {
                dp[l][r] = len;
            }
            for (int m = l; m < r; ++m) {
                if (dp[l][m] != INF && dp[m][r] != INF) {
                    dp[l][r] = min(dp[l][m], dp[m][r]);
                }
            }
        }
    }
    cout << dp[0][n - 1] << '\n';
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int tt = 1;
//    cin >> tt;
    while (tt--) {
        solve();
    }
}