Exceed or not

Write a program that decides whether the product of two integers $a$ and $b$ is greater than $r$.

The first line contains the integers $a$, $b$, and $r$, separated by spaces. ($0 \le a, b \le 10^{20}$, $0 \le r < 2^{63}$)

Except for a value that is 0, no number is given with a leading zero.

If the product of $a$ and $b$ is greater than $r$, print overflow. Otherwise print the product of $a$ and $b$.