n = int(input())
s = input()
a = []
cnt = 0
for i in range(len(s)):
    a.append(s[i])
    if s[i] in ["A","T","C","G"]:
        cnt += 1
while cnt > 0:
    del a[cnt-1]
    cnt = 0
    for i in range(len(a)):
        if a[i] in ["A","T","C","G"]:
            cnt += 1
print(n - len(a))