1.0 KB | 1033 chars
"""
[6012: The Big Dance](https://www.acmicpc.net/problem/6012)
Tier: Silver 3
Category: recursion
"""
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
SYS_INPUT = True
RECURSION_LIMIT = 10 ** 7
SET_RECURSION = False
BLANK = " "
if SET_RECURSION:
sys.setrecursionlimit(RECURSION_LIMIT)
inp = lambda : sys.stdin.readline().rstrip() if SYS_INPUT else input()
mii = lambda : [*map(int,inp().split())]
mfi = lambda : [*map(float,inp().split())]
ii = lambda : int(inp())
fi = lambda : float(inp())
isplit = lambda : inp().split()
p = print
def gcd(a, b): return gcd(b, a % b) if b > 0 else a
def lcm(a, b): return a * b // gcd(a, b)
def f(start, end):
if start == end:
return 0
if start + 1 == end:
return start * end
mid = (start + end) // 2
ret = f(start, mid) + f(mid + 1, end)
# print(start, mid, end, ret)
return ret
def solve():
n = ii()
print(f(1, n))
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()