Let us call a pair of integer numbers *m*-perfect, if at least one number in the pair is greater than or equal to *m*. Thus, the pairs (3, 3) and (0, 2) are 2-perfect while the pair (-1, 1) is not.

Two integers *x*, *y* are written on the blackboard. It is allowed to erase one of them and replace it with the sum of the numbers, (*x* + *y*).

What is the minimum number of such operations one has to perform in order to make the given pair of integers *m*-perfect?
Single line of the input contains three integers *x*, *y* and *m* ( - 10<sup class="upper-index">18</sup> ≤ *x*, *y*, *m* ≤ 10<sup class="upper-index">18</sup>).

Please, do not use the %lld specifier to read or write 64-bit integers in C++. It is preffered to use the cin, cout streams or the %I64d specifier.
a, b, c = map(int, raw_input().split(' '))
if a < 0 and b < 0:
    print(-1)
    quit()
if a < 0 and b >= 0:
    if abs(a)> abs(b):
        print(-1)
        quit()
if b < 0 and a >= 0:
    if abs(b) > abs(a):
        print(-1)
        quit()

ct = 0
while a < c and b < c:
    if a < b:
        a = a + b
    else:
        b = a + b
    ct += 1
print(ct)
