Consider the following transformation involving first order elementary reaction in each step at constant temperature as shown below.

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Some details of the above reactions are listed below.

If the overall rate constant of the above transformation (\( k \)) is given as \( k = \dfrac{k_1 k_2}{k_3} \) and the overall activation energy (\( E_a \)) is \( 400 \, \text{kJ mol}^{-1} \), then the value of \( E_{a3} \) is ______ \( \text{kJ mol}^{-1} \) (nearest integer)