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