#include <bits/stdc++.h>
using namespace std;
vector<long long int> test;
int dp[501][501];
string str;
int cholo(int l, int r) {
  if (l == r)
    return 1;
  else if (l > r)
    return 0;
  int &ret = dp[l][r];
  if (~ret) return ret;
  ret = 1 + cholo(l + 1, r);
  for (int i = l + 1; i <= r; i++) {
    if (str[l] == str[i]) {
      ret = min(ret, cholo(l, i - 1) + cholo(i + 1, r));
    }
  }
  return ret;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int a, b, c, i, j, k, q, p, x, y, sum, ct, ct1, m, l, r, len, x1, y1, mn, n,
      mx, h, sum1, ans;
  char ch;
  double d;
  string str1, str2;
  bool bl, bl1;
  int cs = 1, t;
  while (cin >> n >> str) {
    memset(dp, -1, sizeof dp);
    int tl = cholo(0, n - 1);
    cout << tl << endl;
  }
}
