#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

char S_[100001];

int main(){
    int N; string S;
    cin >> N;
    scanf("%s", S_);
    S = string(S_);
    vi cnt(128);
    each(c, S)cnt[c]++;
    int ans = 0;
    // yuki*[a~h]
    {
        int x = INT_MAX;
        each(c, string("yuki"))smin(x, cnt[c]);
        int y = accumulate(cnt.begin() + 'a', cnt.begin() + 'i', 0);
        smin(y, x);
        ans += y;
        each(c, string("yuki"))cnt[c] -= y;
    }
    // yukii
    {
        int x = INT_MAX;
        each(c, string("yuk"))smin(x, cnt[c]);
        smin(x, cnt['i'] / 2);
        ans += x;
        each(c, string("yuk"))cnt[c] -= x;
        cnt['i'] -= 2 * x;
    }
    // yukj
    {
        int x = INT_MAX;
        each(c, string("yukj"))smin(x, cnt[c]);
        ans += x;
        each(c, string("yukj"))cnt[c] -= x;
    }
    // yukk
    {
        int x = INT_MAX;
        each(c, string("yu"))smin(x, cnt[c]);
        smin(x, cnt['k'] / 2);
        ans += x;
        each(c, string("yu"))cnt[c] -= x;
        cnt['k'] -= 2 * x;
    }
    // yu*[l-t]
    {
        int x = INT_MAX;
        each(c, string("yu"))smin(x, cnt[c]);
        int y = accumulate(cnt.begin()+'l', cnt.begin() + 't' + 1, 0);
        smin(y, x);
        ans += y;
        each(c, string("yu"))cnt[c] -= y;
    }
    // yuu
    {
        int x = min(cnt['y'], cnt['u'] / 2);
        ans += x;
        cnt['y'] -= x;
        cnt['u'] -= 2*x;
    }
    // y*[v-x]
    {
        int x = min(accumulate(cnt.begin() + 'v', cnt.begin() + 'x' + 1, 0), cnt['y']);
        ans += x;
        cnt['y'] -= x;
    }
    // yy
    {
        ans += cnt['y'] / 2;
        cnt['y'] -= cnt['y'] / 2;
    }
    // z
    {
        ans += cnt['z'];
    }
    cout << ans << endl;
}