In a recent Div3 F : https://codeforces.me/contest/1311/problem/F

i made a submission with segtree of size 4*(number of distinct velocity) https://codeforces.me/contest/1311/submission/71877885

it got RE

Then i made segtree of size max it can go i.e 1e6 and it AC https://codeforces.me/contest/1311/submission/71878460

Can someone tell why 4*size is not enough in this case.