#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;
	int val;

	// yukia - yukih
	for (char c = 'a'; c < 'i'; c++) {
		val = min({chars['y'], chars['u'], chars['k'], chars['i'], chars[c]});
		ans += val;
		chars['y'] -= val;
		chars['u'] -= val;
		chars['k'] -= val;
		chars['i'] -= val;
		chars[c] -= val;
	}

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

	// yukj
	for (char c = 'j'; c < 'k'; c++) {

		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;

	// yul - yut
	for (char c = 'l'; c < 'u'; c++) {
		val = min({chars['y'], chars['u'], chars[c]});
		ans += val;
		chars['y'] -= val;
		chars['u'] -= val;
		chars[c] -= val;
	}

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

	// yv - yx
	for (char c = 'v'; c < 'y'; c++) {
		val = min(chars['y'], chars[c]);
		ans += val;
		chars['y'] -= val;
		chars[c] -= val;
	}

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

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

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