4. For any positive integers $n$ and $k (k \leqslant n)$, $f(n, k)$ represents the number of positive integers not exceeding $\left[\frac{n}{k}\right]$ (where [x] denotes the greatest integer not exceeding the real number $x$) that are coprime with $n$. Then $f(100,3)=(\quad)$.
(A) 11
(B) 13
(C) 14
(D) 19