#include <bits/stdc++.h>
using namespace std;
const int maxn = 510;
const int inf = 1e4;
int dp[maxn][maxn];
int main() {
  ios ::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  n--;
  string s;
  cin >> s;
  for (int i = n; i >= 0; i--)
    for (int j = i; j <= n; j++) {
      if (i == j) {
        dp[i][j] = 1;
        continue;
      }
      if (i + 1 == j) {
        dp[i][j] = (s[i] == s[j] ? 1 : 2);
        continue;
      }
      if (s[i] == s[j]) {
        dp[i][j] = min(dp[i][j - 1], dp[i + 1][j]);
      } else {
        dp[i][j] = inf;
        for (int k = i; k < j; k++)
          dp[i][j] = min(dp[i][j], dp[i][k] + dp[k + 1][j]);
      }
    }
  cout << dp[0][n] << endl;
  return 0;
}
