#include <bits/stdc++.h>
using namespace std;
int dp[555][555][2];
char s[555];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) dp[i][i][1] = 0, dp[i][i][0] = 1;
  scanf("%s", s + 1);
  for (int len = 2; len <= n; len++)
    for (int i = 1; i <= n; i++) {
      int j = len + i - 1;
      if (j > n) continue;
      dp[i][j][1] = dp[i][j - 1][0];
      for (int k = i; k < j; k++)
        if (s[k] == s[j]) {
          dp[i][j][1] = min(dp[i][j][1], dp[i][k][1] + dp[k + 1][j][1]);
        }
      dp[i][j][0] = dp[i][j][1] + 1;
      for (int k = i; k < j; k++)
        dp[i][j][0] = min(dp[i][j][0], dp[i][k][1] + dp[k + 1][j][0] + 1);
    }
  cout << dp[1][n][0] << endl;
}
