# Thick Coin

View of neighborhoods in Dusseldorf. 1865.

After graduating in 1860, the St. Petersburg Academy of Arts with high honors, Ivan Shishkin, won the right to travel abroad. In 1861-1865 years the young artist traveled to Europe, where he attended workshops by famous artists.

Commissioned by N.D.Bykov, he wrote in 1865 painting "View of neighborhoods in Dusseldorf", for which he received the title of academician.

In the city n people so much loved the game with the coin, that two outcomes of its flipping (head, tail) were not enough. That's why people decided to construct a thick coin, one of the the outcomes of its flipping is falling on the edge.

Give the minimum thickness that must have the coin with radius <strong>r</strong> so that the probability of its falling on the edge will be 1 / n? The coin has the form of a right cylinder, and its surface is covered with a glue (if the coin touches the ground, it falls either on the edge, or on one of its surfaces).

## Input

Each line is a separate test that contains the integers radius r (0 < r < 100000) of the coin and the integer value of n (1 < n < 100).

## Output

For each test print in a separate line the minimum value of coin thickness. Print the result with 6 digits after the decimal point.