from collections import Counter
N = int(input())
S = input()
C = Counter(S)

ans = C["z"]

for s in "vwx":
    d = min(C["y"], C[s])
    ans += d
    C["y"] -= d
    C[s] -= d

for s in "lmnopqrst":
    d = min(C["y"], C["u"], C[s])
    ans += d
    C["y"] -= d
    C["u"] -= d
    C[s] -= d

d = min(C["y"], C["u"], C["k"], C["j"])
ans += d
C["y"] -= d
C["u"] -= d
C["k"] -= d
C["j"] -= d

tmp = sum(C[s] for s in "abcdefgh")
d = min(C["y"], C["u"], C["k"], C["i"], tmp)
ans += d
C["y"] -= d
C["u"] -= d
C["k"] -= d
C["i"] -= d

d = min(C["y"], C["u"], C["k"], C["i"] // 2)
ans += d
C["y"] -= d
C["u"] -= d
C["k"] -= d

d = min(C["y"], C["u"], C["k"] // 2)
ans += d
C["y"] -= d
C["u"] -= d

d = min(C["y"], C["u"] // 2)
ans += d
C["y"] -= d

ans += C["y"] // 2
print(ans)