#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 1;
const int inf = 1e9 + 1;
int dp[N][N];
int n;
string s;
int solve(int l, int r) {
  if (dp[l][r] != -1) return dp[l][r];
  if (l > r) return 0;
  if (l == r) return dp[l][r] = 1;
  dp[l][r] = 1 + solve(l + 1, r);
  for (int i = l + 1; i <= r; i++) {
    if (s[l] == s[i])
      dp[l][r] = min(dp[l][r], solve(l + 1, i - 1) + solve(i, r));
  }
  return dp[l][r];
}
int main() {
  memset(dp, -1, sizeof(dp));
  cin >> n;
  cin >> s;
  cout << solve(0, n - 1);
}
