Petr is at the upper (nth) floor of a skyscraper, and he wants to go
down to the first floor. The indicator above the elevator door shows that
the elevator is now going down to the first floor and is at the level of the
kth floor. Petr understands that if he goes down several flights of
stairs and calls for the elevator from there he may get to the first floor faster.
Help Petr to determine how many flights of stairs he should go.
The elevator goes up or down one floor in v seconds, and Petr goes down
one flight of stairs in u seconds. When the elevator has reached the
first floor, it has to remain there for 15 seconds; then it can go up.
You may assume that nobody else will call for the elevator. Boarding the
elevator takes 5 seconds. All other delays shouldn't be taken into account.
The single input line contains the numbers n, k, u, and
v (1 < k < n < 100;
0.1 < v < u < 100).
Output the number of the floor which Petr should descend to. If there are
several equivalent variants, output such one in which Petr will go by foot the
50 49 4.8 0.2
Problem Author: Vladimir Yakovlev
Problem Source: IX USU Open Personal Contest (March 1, 2008)