What is an initial element of distance algorithm?

IndexOfSmallestElement = distance(begin(EachRowDistance), smallest);

In the above code when I call a distance algorithm, what will be the initial index of a vector? Does the above code return index starting from 0 or 1?

vector.size() returns total number of element in its container, likewise does the above code return a index starting from 0 or 1?

Example

vec = {1,2,3,4,5}

In the above code is IndexOfSmallestElement 0 or 1 ?