I am reading the book -- Artificial Intelligence a modern approach. I came across this sentence describing the time complexity of uniform cost search

Uniform-cost search is guided by path costs rather than depths, so its complexity is not easily characterized in terms of b and d. Instead, let C be the cost of the optimal solution,7 and assume that every action costs at least ε. Then the algorithm’s worst-case time and space complexity is O(b^(1+C/ε)), which can be much greater than bd.

As to my understanding, C is the cost of the optimal solution, and every action costs at least ε so that C/ε would be the number of steps take to the destination. But I don't know how this complexity has resulted, thanks.