Problems
Convex polygon
Convex polygon
Determine whether a given polygon is convex.
\InputFile
The first line of one number - \textbf{N} (\textbf{3} ≤ \textbf{N} ≤ \textbf{100000}). Next \textbf{N} lines in a pair of numbers - the coordinates of another vertex simple polygon in order to circumvent or counterclockwise. All coordinates are integers modulo not exceeding \textbf{10000}.
\OutputFile
One line of "\textbf{YES}", if given polygon is convex, and "\textbf{NO}" otherwise.
Input example #1
3 0 0 0 1 1 0
Output example #1
YES