N = int(input())
S = input()
cnt = 0
for i in range(N):
    if S[i] != 'U':
        continue
    K = (N - i - 1) // 2
    for j in range(K + 1):
        if S[i + j] == 'M' and S[i + 2 * j] == 'G':
            cnt += 1
print(cnt)