#include <bits/stdc++.h>
using namespace std;
struct Interval {
  int l, r;
};
bool compare(Interval i1, Interval i2) { return (i1.l < i2.l); }
long long int dp[501][501];
int main() {
  long long int n;
  cin >> n;
  string second;
  cin >> second;
  long long int len = second.length();
  for (long long int i = 0; i < (len); ++i) dp[i][i] = 1;
  for (long long int i = 0; i < (len); ++i) {
    for (long long int j = 0; j < (len); ++j)
      if (j < i) dp[i][j] = 0;
  }
  for (long long int r = 0; r < (len); ++r) {
    for (long long int l = 0; l < (r); ++l) {
      if (l == r) continue;
      dp[l][r] = 1 + dp[l][r - 1];
      for (int pos = l; pos <= (r - 1); ++pos) {
        if (second.at(pos) == second.at(r))
          dp[l][r] = min(dp[l][r], dp[l][pos] + dp[pos + 1][r - 1]);
      }
    }
  }
  cout << dp[0][len - 1];
  return 0;
}
