#include <bits/stdc++.h>
using namespace std;
int f[500][500];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  string s;
  cin >> s;
  for (int i = 0; i < n; ++i) {
    f[i][i] = 1;
  }
  for (int len = 1; len < n; ++len) {
    for (int i = 0; i + len < n; ++i) {
      int j = i + len;
      f[i][j] = f[i][j - 1] + 1;
      if (s[j] == s[j - 1]) f[i][j] = f[i][j - 1];
      int value = 0;
      int index = -1;
      for (int k = j - 1; k >= i; --k) {
        if (s[k] == s[j]) {
          f[i][j] =
              min(f[i][j], f[i][k] + ((k == j - 1) ? 0 : f[k + 1][j - 1]));
        }
      }
    }
  }
  cout << f[0][n - 1];
  return 0;
}
