Recently i have started problem solving on atcoder and i found kenkoooo.com very useful.But I am not able to get proper idea of problems difficulty level listed on the website unlike on codeforces(problem ratings).Can anybody please make me understand the problem difficulty relation on atcoder in terms of problem rating at codeforces. For example:- problem rating 1500 on codeforces = ___ problem difficulty on kenkoooo.com