代码：

#include <bits/stdc++.h>
using namespace std;
const int N = 250;
int n, ans = 0, a[N], f[N][N];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    memset(f, -0x3f, sizeof(f));
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        f[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 (f[i][k] == f[k + 1][j])
                {
                    f[i][j] = max(f[i][j], f[i][k] + 1);
                    ans = max(ans, f[i][j]);
                }
        }
    cout << ans;
    return 0;
}