This exact problem is found on the Codeforces OJ on this link:

http://codeforces.com/contest/448/problem/D

Its solution is also fully written on stack overflow on this link:

https://stackoverflow.com/questions/33464901/using-binary-search-to-find-k-th-largest-number-in-nm-multiplication-table

I found several people who blindly copied that code and got AC!. The reason I know this problem was on Stackoverflow was because **I** was the one who asked that question in 2015!!