#include <bits/stdc++.h>
using namespace std;
int dp[500][500] = {{0}};
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  string os;
  cin >> n >> os;
  n = os.size();
  string s;
  for (int i = 0; i < n;) {
    char c = os[i];
    s += c;
    while (os[i] == c) i++;
  }
  n = s.size();
  for (int d = 1; d <= n; d++) {
    for (int i = 0; i <= n - d; i++) {
      int j = i + d - 1;
      if (i == j) {
        dp[i][j] = 1;
        continue;
      }
      dp[i][j] = min(dp[i][j - 1], dp[i + 1][j]) + 1;
      if (s[i] == s[j]) dp[i][j] = min(dp[i][j], dp[i + 1][j - 1] + 1);
      for (int k = i; k < j; k++) {
        dp[i][j] = min(
            dp[i][j], dp[i][k] + dp[k + 1][j] - (s[k] == s[i] && s[k] == s[j]));
      }
    }
  }
  cout << dp[0][n - 1] << '\n';
}
