from collections import Counter
n = int(input())
s = list(input())
scnt = Counter(s)
ans = 0
A = "A"
G = "G"
C = "C"
T = "T"

while True:
  agctcnt = scnt[A] + scnt[G] + scnt[C] + scnt[T]
  if agctcnt == 0:
    print(ans)
    break
  
  s[agctcnt - 1] = ""
  s = list("".join(s))
  scnt = Counter(s)
  ans += 1