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

res = 0

for i in range(N - 1):
    for j in range(i + 1, N):
        if S[i] != 'U' or S[j] != 'M':
            continue
        k = 2 * j - i
        if k < N and S[k] == 'G':
            res += 1

print(res)