N = int(input())
S = input()
ans = 0
L = []
for i in range(N-1):
    if S[i] == 'U':
        L.append(i)
    elif S[i] == 'M':
        for j in range(len(L)-1, -1, -1):
            r = i + i - L[j]
            if r >= N:
                break
            if S[r] == 'G':
                ans += 1
print(ans)