#include<iostream>
#include<algorithm>
using namespace std;

string s;

void read() {
    int n;
    cin >> n >> s;
}


void work() {
    int cnt[128] = {};
    for (int i = 0; i < s.size(); ++i)
        ++cnt[(int)s[i]];
    
    int ans = 0;
    
    int nUse;
    
    // yukk
    nUse = min(min(cnt[(int)'y'], cnt[(int)'u']), cnt[(int)'k'] / 2);
    ans += nUse;
    cnt[(int)'y'] -= nUse;
    cnt[(int)'u'] -= nUse;
    cnt[(int)'k'] -= nUse * 2;
    
    for (int i = 'i' + 1; i < 'k'; ++i) {
        int nUse = min(min(min(cnt[(int)'y'], cnt[(int)'u']), cnt[(int)'k']), cnt[i]);
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[(int)'u'] -= nUse;
        cnt[(int)'k'] -= nUse;
        cnt[i]        -= nUse;
    }

    // yuu
    nUse = min(cnt[(int)'y'], cnt[(int)'u'] / 2);
    ans += nUse;
    cnt[(int)'y'] -= nUse;
    cnt[(int)'u'] -= nUse * 2;

    for (int i = 'k' + 1; i < 'u'; ++i) {
        int nUse = min(min(cnt[(int)'y'], cnt[(int)'u']), cnt[i]);
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[(int)'u'] -= nUse;
        cnt[i]        -= nUse;
    }

    // yy
    nUse = cnt[(int)'y'] / 2;
    ans += nUse;
    cnt[(int)'y'] -= nUse * 2;

    for (int i = 'u' + 1; i < 'y'; ++i) {
        int nUse = min(cnt[(int)'y'], cnt[i]);
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[i]        -= nUse;
    }

    
    ans += cnt[(int)'z'];
    
    cout << ans << endl;
}


int main() {
    read();
    work();
    return 0;
}