Tanishq crosses the river!

The velocity of water current varies as

$\large \begin{cases} {v= (\frac{1}{25})y, ~~~~~~~~~~~~~~~~~~~~~~y \leq 250m} \\ {v= 20- (\frac{1}{25})y, ~~~~~~~~~~~~~y>250m} \end{cases}$

where $y$ is the distance from one bank. The width of the river is $500m$. If Tanishq is crossing the river with constant velocity $5m/s$ relative to water and perpendicular to the current, Find the drift of Tanishq in meters.