Problems
Triangles from Matches
Triangles from Matches
Professor Samodelkin decided to show his mental abilities again from problem "Match model". He started to construct the triangles with matches.
What is the minimal number of matches needs Samodelkin to construct n triangles with side of one match.
Input
One number n (n < 2*109
).
Output
Print the number of used matches.
Input example #1
2
Output example #1
5