#include <bits/stdc++.h>
#define rep(i, a) rep2 (i, 0, a)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) repr2 (i, 0, a)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define asn(a, b, c) fill_n(&(b), sizeof(a) / sizeof(b), c)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int main() {
	int N;
	cin >> N;
	string S;
	cin >> S;

	vector<int> num(26);
	rep (i, S.length()) num[S[i] - 'a']++;
	vector<int> sum(26);
	partial_sum(num.begin(), num.end(), sum.begin());

	int u = num['z' - 'a'];

	// z
	int ans = u;
	u -= u;

	// y*
	u += sum['y' - 'a' - 1] - sum['u' - 'a'];
	int y = min(num['y' - 'a'], u);
	num['y' - 'a'] -= y;
	u -= y;
	u += max(0, num['u' - 'a'] - num['y' - 'a']);
	num['u' - 'a'] -= max(0, num['u' - 'a'] - num['y' - 'a']);

	// yu*	
	u += sum['u' - 'a' - 1] - sum['k' - 'a'];
	int yu = min(min(num['y' - 'a'], num['u' - 'a']), u);
	num['y' - 'a'] -= yu;
	num['u' - 'a'] -= yu;
	u -= yu;
	u += max(0, num['k' - 'a'] - min(num['y' - 'a'], num['u' - 'a']));
	num['k' - 'a'] -= max(0, num['k' - 'a'] - min(num['y' - 'a'], num['u' - 'a']));

	// yuk*
	u += sum['k' - 'a' - 1] - sum['i' - 'a'];
	int yuk = min({num['y' - 'a'], num['u' - 'a'], num['k' - 'a'], u});

	ans += y + yu + yuk;
	cout << ans << endl;

	return 0;
}