from collections import Counter

def read_data():
    N = int(input())
    S = input()
    return N, S

def solve(N, S):
    '''a b c d e f g h [i] j [k] l m n o p q r s t [u] v w x [y] z
    yuki より辞書順で大きい文字列は、
    z で始まるもの
    y で始まり、2文字目がvwxyのいずれか（yをここで使うのが良いのかどうかは悩む。）
    yu で始まり、3文字目がlmnopqrstuのいずれか
    yuk で始まり、4文字目がjk のいずれか
    yuki で始まり、5文字目がabcdefghi のいずれか
    greedy に、上から順に作っていけばよいのか？
    z と yv は確定させてもよさそう。
    残りについては、yukiover, yukii, yukj, yukk, yul, yuu, yy の順に作っていく。
    '''
    c = Counter(S)
    z = c['z']
    y = c['y']
    vwx = c['v'] + c['w'] + c['x']
    u = c['u']
    l2t = sum(c[ch] for ch in 'lmnopqrst')
    k = c['k']
    j = c['j']
    i = c['i']
    a2h = sum(c[ch] for ch in 'abcdefgh')
    
    # z を切り出す
    counts = z
    
    # yv, yw, yx を切り出す
    if y <= vwx:
        return counts + y
    y -= vwx
    counts += vwx
    return counts + solve_yukiover(y, u, l2t, k, j, i, a2h)

def solve_yukiover(y, u, l2t, k, j, i, a2h):
    yukiover = min(y, u, k, i, a2h)
    y -= yukiover
    u -= yukiover
    k -= yukiover
    i -= yukiover
    a2h -= yukiover
    if y == 0:
        return yukiover
    if u == 0:
        return yukiover + y // 2
    if k == 0:
        return yukiover + solve_yul(y, u, l2t)
    if i == 0:
        return yukiover + solve_yukj(y, u, l2t, k, j)
    if a2h == 0:
        return yukiover + solve_yukii(y, u, l2t, k, j, i)

def solve_yukii(y, u, l2t, k, j, i):
    yukii = min(y, u, k, i//2)
    y -= yukii
    u -= yukii
    k -= yukii
    i -= yukii * 2
    if y == 0:
        return yukii
    if u == 0:
        return yukii + y // 2
    if k == 0:
        return yukii + solve_yul(y, u, l2t)
    else:
        return yukii + solve_yukj(y, u, l2t, k, j)

def solve_yukj(y, u, l2t, k, j):
    yukj = min(y, u, k, j)
    y -= yukj
    u -= yukj
    k -= yukj
    j -= yukj
    if y == 0:
        return yukj
    if u == 0:
        return yukj + y // 2
    if k == 0:
        return yukj + solve_yul(y, u, l2t)
    if j == 0:
        return yukj + solve_yukk(y, u, l2t, k)

def solve_yukk(y, u, l2t, k):
    yukk = min(y, u, k//2)
    y -= yukk
    u -= yukk
    k -= yukk * 2
    if y == 0:
        return yukk
    if u == 0:
        return yukk + y // 2
    else:
        return yukk + solve_yul(y, u, l2t)

def solve_yul(y, u, l2t):
    yul = min(y, u, l2t)
    y -= yul
    u -= yul
    l2t -= yul
    if y == 0:
        return yul
    if u == 0:
        return yul + y // 2
    if l2t == 0:
        return yul + solve_yuu(y, u)

def solve_yuu(y, u):
    yuu = min(y, u // 2)
    y -= yuu
    u -= yuu * 2
    if y == 0:
        return yuu
    else:
        return yuu + y // 2

if __name__ == '__main__':
    N, S = read_data()
    print(solve(N, S))