Kata

You throw a ball vertically upwards with an initial speed v0 (in km per hour).

The height h of the ball at each time t is given by $h=v_0\cdot t-0.5\cdot g\cdot t\cdot t\backslash ;\; h\; =\; v\_0\; \backslash cdot\; t\; -\; 0.5\; \backslash cdot\; g\; \backslash cdot\; t\; \backslash cdot\; t\; \backslash ;$, where g is the Earth's gravity $(g\approx 9.81m\mathrm{/}{s}^2)(\; g\; \backslash approx\; 9.81\; \backslash ,\; m/s^2\; )$.

A device is recording at every tenth of second the height of the ball.

For example, with v0 = 15 km/h, the device gets something of the following form: (0, 0.0), (1, 0.367...), (2, 0.637...), (3, 0.808...), (4, 0.881..) ... where the first number is the time in tenths of a second and the second number the height in meter.

Task

Write a function with a parameter v0 (in km per hour) that returns the time in tenth of second of the maximum height recorded by the device.

Examples

Given initial speed v0 = 15 --> should return 4

Given initial speed v0 = 25 --> should return 7

Notes

• Remember to convert the velocity from km/h to m/s or from m/s to km/h when necessary.
• The maximum height recorded by the device is not necessarily the maximum height reached by the ball.