Let function F be defined as F(x)=∫_1^x (e^t)/t dt, x>0 then the value of the integral ∫_1^x (e^t)/(t + a) dt, where a >0, is:

Let function F be defined as $\displaystyle F(x)=\int_1^x \frac{\mathrm{e}^{\mathrm{t}}}{\mathrm{t}} \mathrm{dt}, x>0$ then the value of the integral $\displaystyle \int_1^x \frac{\mathrm{e}^{\mathrm{t}}}{\mathrm{t}+\mathrm{a}} \mathrm{dt}$, where $\displaystyle \mathrm{a}>0$, is :