##Consider the below series :
##
##0,0,2,1,4,2,6,3,8,4,10,5,12,6,14,7,16,8
##This series is a mixture of 2 series
##all the odd terms in this series form even numbers in ascending order
##Every even terms is derived from the previous  term using the formula (x/2)
##Write a program to find the nth term in this series.
##
##The value n in a positive integer that should be read from STDIN
##the nth term that is calculated by the program should be written to STDOUT.
##Other than the value of the nth term no other characters /strings or message should be written to STDOUT.
##
##For example
##if n=10,the 10 th term in the series is to be derived from the 9th term in the series.
##The 9th term is 8 so the 10th term is (8/2)=4. Only the value 4 should be printed to STDOUT.
##You can assume that the n will not exceed 20,000.



num = int(input())
a,b = 0,0

for i in range(1,num+1):
    if (i%2 != 0):
        a = a+2
    else:
        b = b+1

if (num%2 != 0):
    print(int(a-2))
else:
    print(int(b-1))
