Score : 100 points
ButCoder Inc. runs a programming competition site called ButCoder. In this site, a user is given an integer value called rating that represents his/her skill, which changes each time he/she participates in a contest. The initial value of a new user's rating is 0, and a user whose rating reaches K or higher is called Kaiden ("total transmission"). Note that a user's rating may become negative.
Hikuhashi is a new user in ButCoder. It is estimated that, his rating increases by A in each of his odd-numbered contests (first, third, fifth, ...), and decreases by B in each of his even-numbered contests (second, fourth, sixth, ...).
According to this estimate, after how many contests will he become Kaiden for the first time, or will he never become Kaiden?
Input is given from Standard Input in the following format:
K A B
If it is estimated that Hikuhashi will never become Kaiden, print -1
. Otherwise, print the estimated number of contests before he become Kaiden for the first time.
4000 2000 500
5
Each time Hikuhashi participates in a contest, his rating is estimated to change as 0 → 2000 → 1500 → 3500 → 3000 → 5000 → … After his fifth contest, his rating will reach 4000 or higher for the first time.
4000 500 2000
-1
Each time Hikuhashi participates in a contest, his rating is estimated to change as 0 → 500 → -1500 → -1000 → -3000 → -2500 → … He will never become Kaiden.
1000000000000000000 2 1
1999999999999999997
The input and output values may not fit into 32-bit integers.