N = int(input())
S = input()

ans=0
for i in range(N):
    c=S.count("A")+S.count("G")+S.count("C")+S.count("T")
    if c==0:
        break
#    print(c)
    t=S[:c-1]+S[c:]
    S=t
#    print(t)
    ans+=1
print(ans)