Expand a random range from 1-5 to 1-7

Problem:
Given a function which produces a random integer in the range 1 to 5, write a function which produces a random integer in the range 1 to 7.
Solution:

int i;
do
{
  i = 5 * (rand5() - 1) + rand5();  // i is now uniformly random between 1 and 25
} while(i > 21);
// i is now uniformly random between 1 and 21
return i % 7 + 1;  // result is now uniformly random between 1 and 7

Complexity: