Exponential Random Generator in C#

I am trying to write a random generator method which generates random numbers with exponential distribution in C#, i was able to write it in C++, but i don't know the equivalent for C#. Here is my code in c++, Does anybody know the equivalent in C#?

double  rand-exp (double average){
double u;
u = rand() / (RAND_MAX + 1.0);
return -log(1- u) / average;}

Thank in advance