def printM(A):
    for elem in A:
        print(*elem)


kor = [0, 0]
data = [kor]
to = [0, 1]
comands = list(input())
k = 0
for comand in comands:
    if comand == 'R':
        if to == [0,1]:
            to = [1,0]
        elif to == [1, 0]:
            to = [0, -1]
        elif to == [0, -1]:
            to = [-1, 0]
        elif to == [-1, 0]:
            to = [0, 1]
    elif comand == 'L':
        if to == [0,1]:
            to = [-1,0]
        elif to == [1, 0]:
            to = [0, 1]
        elif to == [0, -1]:
            to = [1, 0]
        elif to == [-1, 0]:
            to = [0, -1]
    elif comand == 'S':
        kor = [kor[0] + to[0], kor[1] + to[1]]
        k += 1
        if kor in data:
            print(k)
            break
        data.append(kor)
else:
    print(-1)