#include <bits/stdc++.h>
using namespace std;
int n, i, j;
int mem[505][505];
string s;
int f(int l, int r) {
  int cnt;
  if (l > r) return 0;
  if (l == r) return 1;
  if (mem[l][r]) return mem[l][r];
  cnt = f(l + 1, r) + 1;
  for (int k = l + 1; k <= r; k++) {
    if (s[l] == s[k]) cnt = min(cnt, f(l + 1, k - 1) + f(k, r));
  }
  return mem[l][r] = cnt;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> s;
  cout << f(0, n - 1);
}
