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

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