#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e3 + 10;
char s[maxn];
int n;
int dp[maxn][maxn];
int main(int argc, char const *argv[]) {
  cin >> n;
  scanf("%s", s + 1);
  memset(dp, 0x3f3f3f3f, sizeof dp);
  for (int i = 1; i <= n; i++) dp[i][i] = 1;
  for (int i = 1; i < n; i++) {
    if (s[i] == s[i + 1])
      dp[i][i + 1] = 1;
    else
      dp[i][i + 1] = 2;
  }
  for (int len = 3; len <= n; len++) {
    for (int i = 1; i + len - 1 <= n; i++) {
      int j = i + len - 1;
      if (s[i] == s[j]) {
        dp[i][j] = min(dp[i][j], dp[i + 1][j - 1] + 1);
      } else {
        dp[i][j] = min(dp[i][j], min(dp[i + 1][j], dp[i][j - 1]) + 1);
      }
      for (int k = i; k <= j; k++) {
        dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j] - 1);
      }
    }
  }
  cout << dp[1][n] << endl;
  return 0;
}
