#include <bits/stdc++.h>
using namespace std;
int f[510][510], n;
char str[510];
int main() {
  scanf("%d%s", &n, str + 1);
  for (int i = 1; i <= n; i++) f[i][i] = 1;
  for (int len = 2; len <= n; len++)
    for (int i = 1; i <= n - len + 1; i++) {
      int j = i + len - 1;
      f[i][j] = n + 1;
      for (int k = i; k < j; k++)
        f[i][j] = min(f[i][j], f[i][k] + f[k + 1][j - 1] + (str[j] != str[k]));
    }
  printf("%d\n", f[1][n]);
}
