The root of a cubic equation#4420
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The root of a cubic equation

1 second
128 megabytes
Very easy

Given a cubic equation

a x^3 + b x^2 + c x + d = 0 (a \ne 0)

It is known that this equation has exactly one root. Find it.

Input

Four integers: a, b, c, d~(-1000 \le a, b, c, d \le 1000).

Output

Print the root of the equation with no less than decimal digits.

Examples

Example 1

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Example 2

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