n = int(input())
s = input()

count = 0
sw = True

if s.count("A") + s.count("G") + s.count("C") + s.count("T") == 0:
    print(0)
    sw = False

while sw:
    x = s.count("A") + s.count("G") + s.count("C") + s.count("T")
    
    s = s[:x-1] + s[x:]
    
    x = x = s.count("A") + s.count("G") + s.count("C") + s.count("T")
    
    count += 1
    
    if x == 0:
        print(count)
        sw = False