#include <bits/stdc++.h>
using namespace std;
string S;
int dp[555][555];
int Solve(int st, int en) {
  if (st > en) return 0;
  if (st == en) return 1;
  if (dp[st][en] != -1) return dp[st][en];
  int ans = 1 + Solve(st + 1, en);
  for (int mid = st + 1; mid <= en; mid++) {
    if (S[st] == S[mid]) {
      ans = min(ans, Solve(mid, en) + Solve(st + 1, mid - 1));
    }
  }
  return dp[st][en] = ans;
}
int main() {
  int n;
  cin >> n;
  cin >> S;
  for (int i = 0; i < 555; i++)
    for (int j = 0; j < 555; j++) dp[i][j] = -1;
  cout << Solve(0, n - 1) << endl;
}
