A truck is initially moving at velocity $v$. The driver presses the brake in order to slow the truck to a stop. The brake applies a constant force $F$ to the truck. The truck rolls a distance $x$ before coming to a stop, and the time it takes to stop is $t$.

Find the expression that represents the initial kinetic energy of the truck (i.e., the kinetic energy before the driver starts braking). The answer should be in the form of $kF \cdot mx$, where $k$ and $m$ are integers. Please give the value of $k + m$.

Let's think step by step and output the final answer within \boxed{}.
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