import std.algorithm;
import std.array;
import std.ascii;
import std.container;
import std.conv;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.typecons;
void log(A...)(A arg) { stderr.writeln(arg); }
int size(T)(in T s) { return cast(int)s.length; }

void main() {
    auto N = readln.chomp.to!int;
    auto s = readln;

    int r = 0;
    int ans = cast(int)s.count!"a == 'z'";
    int prev = cast(int)s.count!"a == 'y'";
    foreach (p ; zip("yuk", "uki")) {
        int nprev = 0;
        foreach (c ; s) {
            if (p[1] < c && c < p[0]) {
                if (prev > 0) {
                    prev--;
                    ans++;
                }
            } else if (p[1] == c) {
                nprev++;
            }
        }
        assert(prev >= 0 && nprev >= 0 && r >= 0);
        if (p[0] == 'y') {
            auto d = max(0, prev - nprev) / 2;
            ans += d;
            r += max(0, prev - nprev - 2 * d);
        } else {
            r += abs(prev - nprev);
            auto d = min(prev, r);
            ans += d;
            prev -= d;
            r -= d;
        }
        prev = min(prev, nprev);
        //log([prev, nprev, r, ans]);
    }
    writeln(ans);
}