#include<iostream>
using namespace std;
const int INF = 1<<30;

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;
    
    for (int i = 'y' + 1; i <= 'z'; ++i) {
        int nUse = cnt[i];
        ans += nUse;
        cnt[i] -= nUse;
    }
    
    for (int i = 'u' + 1; i <= 'z'; ++i) {
        int nUse = INF;
        if (i == 'y') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[i]        -= nUse;
    }

    for (int i = 'k' + 1; i <= 'z'; ++i) {
        int nUse = INF;
        if (i == 'y') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        if (i == 'u') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[(int)'u'] -= nUse;
        cnt[i]        -= nUse;
    }

    for (int i = 'i' + 1; i <= 'z'; ++i) {
        int nUse = INF;
        if (i == 'y') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        if (i == 'u') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        if (i == 'k') {
            nUse = min(nUse, cnt[i] / 2);
        }
        else {
            nUse = min(nUse, cnt[i]);
        }
        
        ans += nUse;
        cnt[(int)'y'] -= nUse;
        cnt[(int)'u'] -= nUse;
        cnt[(int)'k'] -= nUse;
        cnt[i]        -= nUse;
    }
    
    cout << ans << endl;
}


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