import math
from decimal import *

def solution(s):
    getcontext().prec = 10000
    sqrt_2 = Decimal(2).sqrt()

    return str(beatty_sum(sqrt_2, int(s)))

def beatty_sum(r, n):
    if n == 0:
        return 0
    if n == 1:
        return 1
    floor_r_n = int(math.floor(r*n))
    
    return natural_number_sum(floor_r_n) - 2 * natural_number_sum(floor_r_n - n) - beatty_sum(r, floor_r_n - n)

def natural_number_sum(n):
    return n*(n+1)/2

def ten(n):
    return 10**n

tests = [
        ['77', '4208'],
        ['1', '1'],
        ['2', '3'],
        ['3', '7'],
        ['4', '12'],
        ['5', '19'],
        ['6', '27'],
        ['7', '36'],
        ['8', '47'],
        ['9', '59'],
        ['10', '73'],
        [ten(100), '0']
        ]


for test in tests:
    result = solution(test[0])
    print(test[0], result == test[1], result, test[1])