#include <bits/stdc++.h>
using namespace std;
int dp[510][510];
int n;
string s;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> s;
  for (int i = 0; i < (n); ++i) dp[i][i] = 1;
  for (int dl = 2; dl <= (n); dl++) {
    for (int a = 0; a < (n); ++a) {
      int b = a + dl - 1;
      if (b > n) break;
      dp[a][b] = dp[a + 1][b] + 1;
      for (int j = a + 1; j <= (b); j++) {
        if (s[a] == s[j]) dp[a][b] = min(dp[a][b], dp[a + 1][j - 1] + dp[j][b]);
      }
    }
  }
  cout << dp[0][n - 1];
  return 0;
}
