248

#include <bits/stdc++.h>

using namespace std;

const int N = 300;

int rangeDP[N][N], A[N];

int main () {
    freopen ("248.in", "r", stdin);
    freopen ("248.out", "w", stdout);
    int n, res = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> A[i];
    for (int i = 1; i <= n; i++)
        rangeDP[i][i] = A[i];
    for (int len = 2; len <= n; len++) {
        for (int i = 1; i + len - 1 <= n; i++) {
            int j = i + len - 1;
            for (int k = i; k < j; k++) {
                if (rangeDP[i][k] == rangeDP[k + 1][j])
                    rangeDP[i][j] = max (rangeDP[i][j], rangeDP[i][k] + 1);
            }
            res = max (res, rangeDP[i][j]);
        }
    }
    cout << res << "\n";
    return 0;
}