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Problems

The angle between the vectors

The angle between the vectors

Time limit 1 second
Memory limit 122 MiB

Calculate the angle between two vectors.

Input data

Four integers x[1],y[1],x[2],y[2] - the coordinates of two nonzero vectors. All values do not exceed 10000 by the absolute value.

Output data

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

Examples

Input example #1
2 1 3 5
Output example #1
0.56673