'''
Problem:
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 n, find the sum of the even-valued terms.
e.g. for n=10, we have {2,8}, sum is 10.
'''

n = int(raw_input().strip())
i=1; j=2; sum=0
while(j<=n):
    if((j&1)==0): #can also use (j%2==0)
        sum+=j
    temp=i
    i=j
    j=temp+i
print sum