题解 | #[NOIP2015]金币#

import math

k=int(input())
c=math.ceil(math.sqrt(2*k))
def get_salary_seq():
    s=[]
    for i in range(c):
        for j in range(i+1):
            s.append(i+1)
            if len(s)==k:
                return s
s=get_salary_seq()
print(sum(s))
# n*(n+1)/2=k
# n**2<2*k and (n+1)**2>2*k