#include <bits/stdc++.h>
#define USACOIN ifstream cin("248.in"); ofstream cout("248.out");

using namespace std;
vector<vector<int>> dp;
vector<int>v;

int main(){
	USACOIN
	ios::sync_with_stdio(false);

	int n, answ = 0;
	cin >> n;

	v.resize(n);
	dp.assign(n, vector<int>(n, 0));
	for(int i = 0; i < n; i++){
		cin >> v[i];
		dp[i][i] = v[i];
		answ = max(answ, v[i]);
	}

	for(int j = 1; j < n; j++){
		for(int i = j-1; i >= 0; i--){ // Creating answer for interval i-j
			for(int k = i; k < j; k++){ // Checking if best answer is merging i-k with k+1-j
				if(dp[i][k] != 0 && dp[k+1][j] != 0 && dp[i][k] == dp[k+1][j]){
					dp[i][j] = dp[i][k]+1;
					answ = max(answ, dp[i][j]);
				}
			}
		}
	}

	cout << answ << '\n';

	return 0;
}