#!/usr/bin/env python3
import collections
# abcdefghijklmnopqrstuvwxyz
#         4 3         2   1
_ = int(input())
cnt = collections.Counter()
for c in input():
    cnt[c] += 1
def take(c, z=None):
    if z is None:
        z = c
    while c <= z:
        if cnt[c]:
            cnt[c] -= 1
            return c
        c = chr(ord(c) + 1)
    return ''
def construct(s):
    acc = ''
    for c in s:
        if c.islower():
            acc += take(c)
        elif c.isupper():
            acc += take(c.lower(), 'z')
    if len(acc) < len(s):
        for c in acc:
            cnt[c] += 1
        return False
    else:
        return True
ans = 0
for s in [ 'yukiA', 'yukJ', 'yuL', 'yV', 'Z' ]:
    while construct(s):
        ans += 1
print(ans)