#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  int n;
  cin >> n;
  string s;
  cin >> s;
  int dp[n][n];
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) dp[i][j] = 1e9;
  for (int l = n - 1; l >= 0; l--)
    for (int r = l; r < n; r++) {
      if (l == r)
        dp[l][r] = 1;
      else
        dp[l][r] = min(r - l + 1, dp[l + 1][r] + 1);
      if (l < n - 1)
        if (s[l + 1] == s[l]) dp[l][r] = min(dp[l][r], dp[l + 1][r]);
      for (int pos = l + 1; pos <= r; pos++)
        if (s[pos] == s[l])
          dp[l][r] = min(dp[l][r], dp[l + 1][pos - 1] + dp[pos][r]);
    }
  cout << dp[0][n - 1] << "\n";
}
