def main():
    N = int(input())
    S = input()
    u = S.find('U')+1
    cnt = 0
    while u:
        m = S.find('M',u)+1
        while m:
            g = m*2 - u
            if g <= N:
                if S[g-1] =='G':
                    cnt +=1
            m = S.find('M',m)+1
        u = S.find('U',u)+1
    print(cnt)
main()