#include <bits/stdc++.h>
using namespace std;
int dp[510][510];
char str[510];
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", str + 1);
  memset(dp, 0, sizeof(dp));
  for (int i = 1; i <= n; i++) {
    dp[i][i] = 1;
  }
  for (int L = 2; L <= n; L++) {
    for (int i = 1; i + L - 1 <= n; i++) {
      int j = i + L - 1;
      dp[i][j] = n;
      for (int k = i; k < j; k++) {
        if (str[k] == str[j]) {
          dp[i][j] = min(dp[i][j], dp[i][k] + dp[k + 1][j] - 1);
        } else {
          dp[i][j] = min(dp[i][j], dp[i][k] + dp[k + 1][j]);
        }
      }
    }
  }
  printf("%d\n", dp[1][n]);
  return 0;
}
