#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>

#define INF 1000000000

using namespace std;
typedef long long ll;

int main(void) {
    int z = 0, y = 0, v = 0, u = 0, l = 0, k = 0, j = 0, i = 0, a = 0;
    int N;
    string s;
    cin >> N;
    cin >> s;
    for (int p = 0; p < N; p++) {
        if (s[p] == 'z') z++;
        else if (s[p] == 'y') y++;
        else if (s[p] > 'u') v++;
        else if (s[p] == 'u') u++;
        else if (s[p] > 'k') l++;
        else if (s[p] == 'k') k++;
        else if (s[p] > 'i') j++;
        else if (s[p] == 'i') i++;
        else a++;
    }
    int ans = 0;
    while (y && u && k && i && a) {
        y--; u--; k--; i--; a--; ans++;
    }
    while (y && u && k && i >= 2) {
        y--; u--; k--; i-=2; ans++;
    }
    while (y && u && k && j) {
        y--; u--; k--; j--; ans++;
    }
    while (y && u && k >= 2) {
        y--; u--; k-=2; ans++;
    }
    while (y && u && l) {
        y--; u--; l--; ans++;
    }
    while (y && u >= 2) {
        y--; u-=2; ans++;
    }
    while (y && v) {
        y--; v--; ans++;
    }
    while (y >= 2) {
        y-=2; ans++;
    }
    while (z) {
        z--; ans++;
    }
    cout << ans << endl;
    return 0;
}