Chef And Numbers

Chef has been given two integers $n$ and $m$. He creates two lists of integers — the first one having integers from $1$ to $n$ and the second list having integers from $1$ to $m$. Now, Chef wants to count the number of integral pairs can be chosen, one number of the pair from the first list and the other number from the the second list, such that $5$ divides the sum of the chosen numbers. Chef