Problems

# The angle between the vectors

# The angle between the vectors

Calculate the angle between two vectors.

#### Input

Four integers `x`

,_{1}`y`

,_{1}`x`

,_{2}`y`

- the coordinates of two nonzero vectors. All values do not exceed _{2}**10000** by the absolute value.

#### Output

Print the value of an undirected angle between vectors with **5** decimal places in the interval [**0**; **π**].

Input example #1

2 1 3 5

Output example #1

0.56673