#include <bits/stdc++.h>
using namespace std;
const int N = 500;
int n, f[N][N];
string s;
int main() {
  cin >> n >> s;
  for (int i = 1; i < n; i++)
    for (int j = 0; j + i < n; j++) {
      f[j][j + i] = f[j + 1][j + i] + 1;
      for (int k = j; k <= j + i; k++)
        if (s[k] == s[j])
          f[j][j + i] = min(f[j][j + i], f[j][k - 1] + f[k][j + i]);
    }
  cout << f[0][n - 1] + 1;
  return 0;
}
