#include <bits/stdc++.h>
using namespace std;
int n;
char s[508];
int dp[508][508];
int main() {
  scanf("%d %s", &n, s + 1);
  memset(dp, 0x3f, sizeof(dp));
  for (int l = 1; l <= n; ++l) dp[l][l] = 1;
  for (int Len = 2; Len <= n; ++Len) {
    for (int l = 1; l + Len - 1 <= n; ++l) {
      int r = l + Len - 1;
      for (int k = l; k < r; ++k) {
        dp[l][r] = min(dp[l][r], dp[l][k] + dp[k + 1][r] - (s[l] == s[r]));
      }
    }
  }
  cout << dp[1][n] << endl;
  return 0;
}
