#include <bits/stdc++.h>
using namespace std;
string s;
int N,n,a_h,i,j,k,l_t,u,v_x,y,z;
int main(){
    cin >> N >> s;
    int res = 0;
    for(n=0;n<N;n++){
        char &c = s[n];
        if(c<='h')a_h++;
        else if(c<='i')i++;
        else if(c<='j')j++;
        else if(c<='k')k++;
        else if(c<='t')l_t++;
        else if(c<='u')u++;
        else if(c<='x')v_x++;
        else if(c<='y')y++;
        else if(c<='z')z++;
    }
    n = min({y,u,k,i,a_h}); res+=n,y-=n,u-=n,k-=n,i-=n,a_h-=n;
    n = min({y,u,k,i/2});   res+=n,y-=n,u-=n,k-=n,i-=n*2;
    n = min({y,u,k,j});     res+=n,y-=n,u-=n,k-=n,j-=n;
    n = min({y,u,k/2});     res+=n,y-=n,u-=n,k-=n*2;
    n = min({y,u,l_t});     res+=n,y-=n,u-=n,l_t-=n;
    n = min({y,u/2});       res+=n,y-=n,u-=n*2;
    n = min({y,v_x});       res+=n,y-=n,v_x-=n;
    res += y/2 + z;
    cout<<res<<endl;
}