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*10`

).^{9}

#### Output

Print the number of used matches.

Input example #1

2

Output example #1

5