import sequtils,strutils,math
var
    N = stdin.readline.parseInt
    s = stdin.readline
    cnt : array['a'..'z', int]
    ans,j : int
for c in s:
    cnt[c] += 1
proc csum(A : array['a'..'z', int]; a, b : char): int =
    result = 0
    for c in a..b:
        result += A[c]
block main:
    ans += cnt['z']
    cnt['z'] = 0
    j = min(@[cnt['y'], cnt['u'], cnt['k'], cnt['i'], cnt.csum('a', 'h')])
    ans += j
    cnt['y'] -= j
    cnt['u'] -= j
    cnt['k'] -= j
    cnt['i'] -= j
    j = min(@[cnt['y'], cnt['u'], cnt['k'], cnt['i'] div 2])
    ans += j
    cnt['y'] -= j
    cnt['u'] -= j
    cnt['k'] -= j
    cnt['i'] -= j * 2
    j = min(@[cnt['y'], cnt['u'], cnt['k'] div 2])
    ans += j
    cnt['y'] -= j
    cnt['u'] -= j
    cnt['k'] -= j * 2
    j = min(@[cnt['y'], cnt['u'], cnt.csum('l', 't')])
    ans += j
    cnt['y'] -= j
    cnt['u'] -= j
    for c in 'l'..'t':
        if j > cnt[c]:
            j -= cnt[c]
            cnt[c] = 0
        else:
            cnt[c] -= j
            j = 0
    j = min(cnt['y'], cnt['u'] div 2)
    ans += j
    cnt['y'] -= j
    cnt['u'] -= j * 2
    j = min(cnt['y'], cnt.csum('v', 'x'))
    #echo j
    ans += j
    cnt['y'] -= j
    for c in 'v'..'x':
        if j > cnt[c]:
            j -= cnt[c]
            cnt[c] = 0
        else:
            cnt[c] -= j
            j = 0
    j = cnt['y'] div 2
    ans += j
#[for c,i in cnt:
    echo c, " ", i]#
echo ans