#include <iostream>
#include <algorithm>
#include <climits>
#include <cstring>
#include <string>
#define N_MAX 10000
using namespace std;

int kai(int n)
{
	if (n > 0)
		return n *kai(n - 1);
	else
		return 1;
}

int main()
{
	int N, ans = 0;
	char S[N_MAX];
	cin >> N >> S;

	//ごり押してみる
	for (int i = 0; i < N; ++i)
	{
		if (S[i] > 'y')
		{
			++ans;
			S[i] = 0;
		}
		else if (S[i] == 'y')
			for (int j = 0; j < N; ++j)
			{
				if (j == i)
					continue;
				else if (S[j] > 'u')
				{
					++ans;
					S[j] = S[i] = 0;
				}
				else if (S[j] == 'u')
					for (int k = 0; k < N; ++k)
					{
						if (k == i || k == j)
							continue;
						else if (S[k] > 'k')
						{
							++ans;
							S[k] = S[j] = S[i] = 0;
						}
						else if (S[k] == 'k')
							for (int l = 0; l < N; ++l)
							{
								if (l == i || l == j || l == k)
									continue;
								else if (S[l] > 'i')
								{
									++ans;
									S[l] = S[k] = S[j] = S[i] = 0;
								}
							}
					}

			}
	}

	cout << ans;

	return 0;
}