#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>

using namespace std;

int main() {
	int n;
	string s;
	vector<int> chars(255, 0);

	cin >> n >> s;

	for (int i = 0; i < n; i++) {
		chars[s[i]]++;
	}

	int ans = 0;

	ans += chars['z'];
	chars['z'] = 0;

	int val;
	// yu
	for (char c = 'z'; c > 'u'; c--) {
		if (c == 'y') {
			continue;
		}

		val = min(chars['y'], chars[c]);
		ans += val;
		chars['y'] -= val;
		chars[c] -= val;
	}

	// yuk
	for (char c = 'z'; c > 'k'; c--) {
		if (c == 'y' || c == 'u') {
			continue;
		}

		val = min({chars['y'], chars['u'], chars[c]});
		ans += val;
		chars['y'] -= val;
		chars['u'] -= val;
		chars[c] -= val;
	}

	// yuki
	for (char c = 'z'; c > 'i'; c--) {
		if (c == 'y' || c == 'u' || c =='k') {
			continue;
		}

		val = min({chars['y'], chars['u'], chars['k'], chars[c]});
		ans += val;
		chars['y'] -= val;
		chars['u'] -= val;
		chars['k'] -= val;
		chars[c] -= val;
	}

	// yukk
	val = min({chars['y'], chars['u'], chars['k'] / 2});
	ans += val;
	chars['y'] -= val;
	chars['u'] -= val;
	chars['k'] -= val * 2;

	// yuu
	val = min(chars['y'], chars['u'] / 2);
	ans += val;
	chars['y'] -= val;
	chars['u'] -= val * 2;

	// yy
	val = chars['y'] / 2;
	ans += val;
	chars['y'] -= val * 2;

	cout << ans << endl;
	return 0;
}