#include <bits/stdc++.h>
using namespace std;
int n;
char c[510];
int f[510][510];
int main() {
  scanf("%d%s", &n, &c);
  for (register int i = 0; i < n; i++) f[i][i] = 1;
  for (register int i = 1; i < n; i++)
    for (register int j = 0; j < i; j++) {
      f[j][i] = 1 << 30;
      for (register int k = j; k < i; k++)
        f[j][i] =
            min(f[j][i], f[j][k] + f[k + 1][i - 1] + 1 - (int)(c[i] == c[k]));
    }
  printf("%d", f[0][n - 1]);
  return 0;
}
