/* Problem URL: https://usaco.org/index.php?page=viewproblem2&cpid=647 */

#include <bits/stdc++.h>

using namespace std;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	ifstream in("248.in");
	ofstream out("248.out");

	int n;
	in >> n;
	vector<long long> el(n);
    in >> el;

	vector<vector<long long>> dp(n, vector<long long>(n, 0));
	long long ans = 0;
	for (size_t i = 0; i < n; i++) {
		dp[i][i] = el[i];
		ans = max(ans, dp[i][i]);
	}

	for (size_t j = 1; j < n; j++) {
		for (int i = j - 1; i >= 0; i--) {
			for (size_t k = i; k < j; k++) {
				if (dp[i][k] != 0 && dp[k + 1][j] != 0 && dp[i][k] == dp[k + 1][j]) {
				    rmax(dp[i][j], dp[i][k] + 1);
				}
			}
		    rmax(ans, dp[i][j]);
		}
	}

	out << ans << '\n';
}