1019 : New Tortoise and the Hare

Description

The tortoise and the hare agreed to race again. The hare intends to let the tortoise run for a while, and then catch up with it before the finish line.

L，vt，vh，p respectively represent the length of the track, the speed of the tortoise (per second), the speed of the hare (per second), and the distance the tortoise has traveled when the hare starts.

Can the hare catch up with the tortoise?

Input

There are multiple test cases. Each line contains four integers L，vt，vh，p correspondingly.

10 <= L <= 1000, 1 <= vt < vh <= 1000, 1 <= p <= L.

The cases ends with EOF.

Output

Output a number a line corresponding to each case.

If the hare can catch up with the tortoise before (include) the finish line, the output is the time the hare need to catch up with the tortoise. The result should be accurated to two decimal places.

Otherwise, output -1.

Sample

10 1 2 3
10 1 2 5
10 1 2 6
11 2 5 4

3.00
5.00
-1
1.33

Hint

EOF means the end of the file. In C language, we could use:

while(scanf("%d%d%d%d", &L, &vt, &vh, &p) != EOF)
{
    // Do what you need.
}

to recognise it.

Source

Author

CSGrandeur