#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vc = vector<char>;
using vvc = vector<vc>;
const ll mod = 1e9 + 7, inf = 1e18;
vvi dp(501, vi(501, -1));
string s;
int solve(int i, int j) {
  if (i == j) return 1;
  if (i > j) return 0;
  if (dp[i][j] != -1) return dp[i][j];
  int ans = solve(i + 1, j) + 1;
  for (int k = i + 1; k <= j; k++) {
    if (s[i] == s[k]) ans = min(ans, solve(i + 1, k - 1) + solve(k, j));
  }
  return dp[i][j] = ans;
}
int main() {
  int n;
  cin >> n >> s;
  cout << solve(0, n - 1);
  return 0;
}
