#include <bits/stdc++.h>
using namespace std;
const int N = 505;
int dp[N][N];
int main() {
  memset(dp, 0, sizeof dp);
  int n;
  cin >> n;
  string s;
  cin >> s;
  for (int i = 0; i < n; i++) dp[i][i] = 1;
  for (int len = 2; len <= n; len++) {
    for (int i = 0; i < n; i++) {
      int j = i + len - 1;
      if (j >= n) break;
      dp[i][j] = 1 + dp[i + 1][j];
      for (int k = i + 1; k <= j; k++) {
        if (s[k] == s[i]) {
          dp[i][j] = min(dp[i][j], dp[i + 1][k - 1] + dp[k][j]);
        }
      }
    }
  }
  cout << dp[0][n - 1];
  return 0;
}
