Ok, I give up, I have tried with $u$-substitution and integration by parts but I can't solve it. The integral is:
$\int{\frac{e^x dx}{1+e^{2x}}}$
I have tried $u=e^x$, $u=e^{2x}$ and also integration by parts but I can't solve it. The result should be:
$\arctan(e^x)$