Paying optimally

The currency of Dholakpur is pretty awesome. There notes have values 1, C, C2, C3 ... . The sequence goes on till infinity, so notes have unbounded values. Little Bheem is a resident of Dholakpur and runs a Laddu shop. He always keeps infinite number of notes of each value with him, but pays using minimum number of notes. For example, if C = 5 and he has to pay 32 rupees, he will pay using one no