#include <bits/stdc++.h>
using namespace std;
int f[505][505], n;
char s[505];
int main() {
	cin >> n >> s+1;
	for (int l = 1; l <= n; l++) {
		for (int i = 1; i+l-1 <= n; i++) {
			int j = i + l - 1;
			if (i == j) f[i][j] = 1;
			else {
				f[i][j] = f[i+1][j] + 1;
				for (int k = i+1; k <= j; k++)
					if (s[i] == s[k])
						f[i][j] = min(f[i][j], f[i+1][k] + f[k+1][j]);
			}
		}
	}
	cout << f[1][n] << endl;
	return 0;
}