If we choose an Amperian loop containing both the wires, then the magnetic field along that loop will turn out to be zero as the wires carry currents in the opposite direction and the total current turns out to be lesser than the maximum of that of the two wires. And if the magnitudes of currents are the same then the total current in that loop turns out to be zero. If they are kept very close together, this will hold for even very small Amperian loops. Thus twisting two wires, which carry currents in the opposite directions, minimizes the magnetic field produced and can even cancel it out.

denotes current going perpendicularly inside the screen.

denotes current coming perpendicularly out of the screen.

If this both currents are equal in magnitude then the total current enclosed by the Amperian Loop C will be zero.