n = int(input())
s = "#" + input()
c = 0
for i in range(n+1):
    if s[i] in ["A","C","G","T"]:
        c += 1

if c == 0:
    print(0)
    exit()

idx = c
ans = 0
while c:
    if s[idx] not in ["A","C","G","T"]:
        idx += 1
        ans += 1
    else:
        idx += 1
        c -= 1
        ans += 1
        while c:
            if s[c] not in ["A","C","G","T"]:
                ans += 1
                break
            else:
                c -= 1
                ans += 1

print(ans)