#include <bits/stdc++.h>
using namespace std;
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
template <class T>
void dispvector(vector<T> v) {
  for (int i = 0; i < v.size(); i++) cout << v[i] << " ";
  cout << "\n";
}
template <class T>
void disparray(T *v, int n) {
  for (int i = 0; i < n; i++) cout << v[i] << " ";
  cout << "\n";
}
template <class T>
int sizeofarr(T *v) {
  return sizeof(v) / sizeof(T);
}
signed main(int argc, char **argv) {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n;
  cin >> n;
  vector<long long int> arr(n);
  for (long long int i = 0; i < n; i++) cin >> arr[i];
  int dp[505][505];
  memset(dp, -1, sizeof(dp));
  for (long long int g = 0; g < n; g++) {
    for (long long int i = 0, j = g; i < n - g; i++, j++) {
      if (g == 0) {
        dp[i][j] = arr[i];
      } else {
        for (long long int k = i; k < j; k++) {
          if (dp[i][k] != -1 && dp[i][k] == dp[k + 1][j])
            dp[i][j] = dp[i][k] + 1;
        }
      }
    }
  }
  int dp2[505];
  for (long long int i = 0; i < n; i++) dp2[i] = i + 1;
  for (long long int i = 0; i < n; i++) {
    for (long long int j = 0; j <= i; j++) {
      if (dp[j][i] != -1) {
        if (j == 0)
          dp2[i] = 1;
        else
          dp2[i] = min(dp2[i], dp2[j - 1] + 1);
      }
    }
  }
  cout << dp2[n - 1] << "\n";
  return 0;
}
