#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define UNIQ(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<ld> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

int n;
string s;

int solve() {
    int num[9];
    memset(num, 0, sizeof(num));
    for (int i = 0; i < n; i++) {
        if (s[i] == 'y') num[0]++;
        else if ('v' <= s[i] && s[i] <= 'x') num[1]++;
        else if (s[i] == 'u') num[2]++;
        else if ('l' <= s[i] && s[i] <= 't') num[3]++;
        else if (s[i] == 'k') num[4]++;
        else if (s[i] == 'j') num[5]++;
        else if (s[i] == 'i') num[6]++;
        else if (s[i] == 'z') num[7]++;
        else num[8]++;
    }

    int res = 0;
    res += num[7];
    int d = min(num[0], num[1]);
    res += d;
    num[0] -= d; num[1] -= d;
    d = min(num[0], min(num[2], num[3]));
    res += d;
    num[0] -= d; num[2] -= d; num[3] -= d;
    d = min(min(num[0], num[2]), min(num[4], num[5]));
    res += d;
    num[0] -= d; num[2] -= d; num[4] -= d; num[5] -= d;
    d = min(min(num[0], num[2]), min(num[4], num[6]));
    d = min(d, num[8]+num[6]-d);
    res += d;
    d = min(num[0], min(num[2], num[4]/2));
    res += d;
    num[0] -= d; num[2] -= d; num[4] -= 2*d;
    d = min(num[0], num[2]/2);
    res += d;
    num[0] -= d; num[2] -= 2*d;
    d = num[0]/2;
    res += d;
    num[0] -= 2*d;
    return res;
}

void input() {
    cin >> n >> s;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}