0027. Iteration

Имя входного файла:	iterate.in
Имя выходного файла:	iterate.out
Ограничение по времени:	2 s
Ограничение по памяти:	64 megabytes

Misha has written a program that solves a difficult problem using iterative method. Now he wants to estimate the number of iterations.

His method uses a sequence z_i as its part. This sequence is constructed according the following rules. The first number in sequence is a given real number z₀. The subsequent numbers are calculated using formula . The method stops if the value of z_i is negative. It is guaranteed there will be neither division by zero nor zero-valued z_i before termination condition.

Write a program that evaluates the number of the first negative member of this sequence.

Input file

Input file consists of three numbers: A, B (|A|, |B| ≤ 10⁸) and z₀. z₀ is a real number with no more than 9 digits after decimal point. Also z₀ will not have more than 9 significant digits or exceed 10⁶ by its absolute value. A and B are integer numbers.

Output file

Write only one integer number n – the minimal n satisfying condition z_n<0. If all numbers in the sequence will be positive, display -1.

Examples:

iterate.in	iterate.out
1 1 2	1

Источник: Petrozavodsk training camp, Summer 2002. Startup contest
Автор: Andrew Lopatin, Nick Durov

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