import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv, std.math, std.random;
import std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!long;

  auto k = n / 2;

  writeln((k + 1) * (n - k + 1) - 1);
}