input()
s=input()
loop_count=0
while True:
    t=s.count("A")+s.count("T")+s.count("G")+s.count("C")
    if t==0:
        break
    elif len(s)==t:
        loop_count=loop_count+len(s)
        break
    else:
        s=s[0:t-1]+s[t:]
        loop_count=loop_count+1
print(loop_count)