Mechanism of a hypothetical reaction.

$X_2+Y_2\to 2XY$ is given below

$\text{(a)}{X}_2\rightleftharpoons X+X\left(\text{fast}\right)$

$\text{(b)}X+Y_2\to XY+Y\left(\text{slow}\right)$

$\text{(c)}X+Y\to XY\left(\text{fast}\right)$

The overall order of the reaction will be