Consider ordinary differential equations given by
$\begin{array}{l} \dot{x}_{1}(t)=2 x_{2}(t) \\ \dot{x}_{2}(t)=r(t) \end{array}$
with initial conditions $x_{1}(0)=1$ and $x_{2}(0)=0$.
If $r(t)=\begin{cases}1, & t \geq 0 \\ 0, & t<0\end{cases}$, then at $t=1, x_{1}(t)=$ $\_\_\_\_\_\_\_\_\_$ (round off to the nearest integer).
