#include<bits/stdc++.h>
using namespace std;
#define fr(i, a, b) for (int i = a; i <= b; i++)
typedef long long ll;
typedef unsigned long long ull;
typedef double dou;
typedef pair<int, int> pii;
const int maxn=250;
const ll inf = 1e9 + 5;
const ll mod = 1e9 + 7;
int num[maxn];
int dp[maxn][maxn];
void  solve(){
    int n;
    cin >> n;
    for (int i = 1; i <= n;i++)
    {
        cin >> num[i];
        dp[i][i] = num[i];
    }
    for (int len = 1; len < n;len++)
    {
        for (int i = 1; i+len <= n; i++)
        {
            int j = i + len;
            for (int k = i; k < i + len&&k<j;k++)
            {
                //cout << k + 1 << ' ' << j << ' ' << dp[i][k] << ' ' << dp[k + 1][j] << endl;
                if(dp[i][k]==dp[k+1][j]){
                    dp[i][j] = max(dp[i][j], dp[i][k] + 1);
                }
                else {
                    dp[i][j] = max(dp[i][j], max(dp[i][k], dp[k + 1][j]));
                }
            }
        }
    }
    cout << dp[1][n] << endl;
}

int main()
{
    ios::sync_with_stdio(false);
    int t=1;
    //cin >> t;
    //t = 1;
    while(t--)
    {
        solve();
    }
    system("pause");
    return 0;
}