import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	String yuki = "yuki";

	void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		String str = sc.next();
		int abcdefgh = 0, i = 0, j = 0, k = 0, lmnopqrst = 0, u = 0, vwx = 0, y = 0, z = 0;

		for (int t = 0; t < str.length(); ++t) {
			if (str.charAt(t) - 'i' < 0)
				++abcdefgh;
			else if (str.charAt(t) == 'i') {
				++i;
			} else if (str.charAt(t) - 'j' == 0)
				++j;
			else if (str.charAt(t) - 'k' == 0)
				++k;
			else if (str.charAt(t) - 'l' >= 0 && str.charAt(t) - 't' <= 0)
				++lmnopqrst;
			else if (str.charAt(t) - 'u' == 0)
				++u;
			else if (str.charAt(t) - 'v' >= 0 && str.charAt(t) - 'x' <= 0)
				++vwx;
			else if (str.charAt(t) == 'y')
				++y;
			else if (str.charAt(t) == 'z')
				++z;
			else {
				tr(str.charAt(t));
				throw new AssertionError();
			}
		}
		int ans = 0;
		while (y > 0 && u > 0 && k > 0 && i > 0 && abcdefgh > 0) {
			++ans;
			--y;
			--u;
			--k;
			--i;
			--abcdefgh;
		}
		while (y > 0 && u > 0 && k > 0 && i >= 2) {
			++ans;
			--y;
			--u;
			--k;
			i -= 2;
			--abcdefgh;
		}
		while (y > 0 && u > 0 && k > 0 && j > 0) {
			++ans;
			--y;
			--u;
			--k;
			--i;
			--j;
		}
		while (y > 0 && u > 0 && k >= 2) {
			++ans;
			--y;
			--u;
			k -= 2;
		}
		while (y > 0 && u > 0 && lmnopqrst > 0) {
			++ans;
			--y;
			--u;
			--lmnopqrst;
		}
		while (y > 0 && u >= 2) {
			++ans;
			--y;
			u -= 2;
		}
		while (y > 0 && vwx > 0) {
			++ans;
			--y;
			--vwx;
		}
		while (y >= 2) {
			++ans;
			y -= 2;
		}
		while (z > 0) {
			++ans;
			--z;
		}
		System.out.println(ans);
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}