#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
int n;
string second;
int dp[505][505];
int calc(int i, int j) {
  if (dp[i][j] != 0) return dp[i][j];
  if (i == j) return 1;
  if (i > j) return 0;
  int res = 1000000000;
  res = min(res, 1 + calc(i + 1, j));
  for (int k = (i + 1); k <= (signed)(j); k++) {
    if (second[i] == second[k]) {
      res = min(res, calc(i + 1, k - 1) + calc(k, j));
    }
  }
  dp[i][j] = res;
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> second;
  cout << calc(0, n - 1) << "\n";
  return 0;
}
