'''Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued term0s.
'''
li=[]
li.append(1)
li.append(1)
n= int(input())
s=0
for i in range(n):
    if((li[len(li)-1]+li[len(li)-2])%2)
        s=s+(li[len(li)-1]+li[len(li)-2])
print(s)
      
