#include <bits/stdc++.h>
using namespace std;
int n;
string s;
int dp[501][501];
int memo(int l, int r) {
  if (l > r)
    return 0;
  else if (l == r)
    return 1;
  else if (dp[l][r] != -1)
    return dp[l][r];
  int best = 10000;
  for (int i = l + 1; i <= r; i++) {
    if (s[i] == s[l]) best = min(best, memo(l + 1, i - 1) + memo(i, r));
    best = min(best, 1 + memo(l + 1, r));
  }
  return dp[l][r] = best;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> n;
  cin >> s;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      dp[i][j] = -1;
    }
  }
  cout << memo(0, n - 1);
}
