#include <bits/stdc++.h>
using namespace std;
char s[505];
int n, f[505][505];
int main() {
  ios::sync_with_stdio(false);
  memset(f, 127 / 3, sizeof(f));
  int i, l, r, j;
  cin >> n;
  cin >> s + 1;
  for (i = 1; i <= n; i++) f[i][i] = 1, f[i][i - 1] = 0;
  for (i = 2; i <= n; i++)
    for (l = 1; l <= n - i + 1; l++) {
      r = l + i - 1;
      f[l][r] = f[l + 1][r] + 1;
      for (j = l + 1; j <= r; j++)
        if (s[l] == s[j]) f[l][r] = min(f[l][r], f[l + 1][j - 1] + f[j][r]);
    }
  cout << f[1][n];
  return 0;
}
