def min(a, b):
    return a if a <= b else b

n = int(input())
s = input()
s_list = list(s)

num_M = s_list.count('M')
checked_M = 0
count = 0

while checked_M != num_M:
    M_index = s_list.index('M')
    distance = min(M_index - 0, (n - 1) - M_index)
    ss_list = s_list[M_index - distance : M_index + distance + 1]
#     print('ss_list before: {}'.format(ss_list))
    num_U = ss_list.count('U')
    M_index_ss = ss_list.index('M')
    for i in range(num_U):
        U_index = ss_list.index('U')
        if U_index > M_index_ss:
            break
        else:
            ss_list[U_index] = 'x'
            distance_ss = M_index_ss - U_index
#             print('M_index_ss: {}'.format(M_index_ss))
#             print('U_index: {}'.format(U_index))
#             print('distance_ss: {}'.format(distance_ss))
            if ss_list[M_index_ss + distance_ss] == 'G':
                count += 1
#     print('ss_list after: {}'.format(ss_list))
#     print('count: {}'.format(count))
    # after founding 'umg'
    s_list[M_index] = 'x'
    checked_M += 1
    
print(count)