#include <bits/stdc++.h>
long long power(long long a, long long b, long long mod);
using namespace std;
const double eps = 1e-8;
const double pi = acos(-1.0);
const long long INF = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
const int N = 500 + 5;
int n;
int dp[N][N];
char s[N];
void INIT() {}
void solve() {
  INIT();
  cin >> (s + 1);
  memset(dp, 0, sizeof(dp));
  for (int i = 1; i <= n; i++) dp[i][i] = 1;
  for (int len = 2; len <= n; len++) {
    for (int i = 1, j = i + len - 1; j <= n; i++, j++) {
      dp[i][j] = 1 + dp[i + 1][j];
      for (int k = i + 1; k <= j; k++) {
        if (s[i] == s[k]) dp[i][j] = min(dp[i][j], dp[i][k - 1] + dp[k + 1][j]);
      }
    }
  }
  cout << (dp[1][n]) << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  while (cin >> n) {
    solve();
  }
  return 0;
}
long long power(long long a, long long b, long long mod) {
  long long ans = 1;
  while (b) {
    if (b % 2) ans = ans * a % mod;
    a = a * a % mod;
    b = b / 2;
  }
  return ans;
}
