Number Theory Level 1

$\begin{array} {c c c } & & \color{green}{C} \\ + & \color{green}{C} & \color{green}{C} \\ \hline & \color{purple}{D} & 4 \\ \end{array}$

In the above cryptogram, $$\color{green}{C}$$ and $$\color{purple}{D}$$ represent distinct digits. What is the value of $$\color{green}{C}$$?

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