I am solving this question Question Solution

I did run this on command line. It gives correct answer & runs fine. Can anyone help with this error?

I am newbie in the competitive programming community. I have solved a few problems with difficulty less than 1200 mostly with tags greedy, math, implementation. Here are my submissions Then I started to move on with different tags starting from data structures But now, I cannot solve those problems (tagged data structures) , though I seem to understand those questions but I cannot code most of the solution... still there were some problems on which I got AC, but they seem to have execution time > 1000 ms which I think are not efficient, right ? Can anyone please help me on how to move ahead in this journey ? It would be very good. More specifically I want to know how to solve problems ahead with possibly more difficulty and varying tags, or is there something wrong with my approach ?