8393. 합

solution 1 : 64ms

List = list(range(int(input()), 0, -1))
print(sum(List))

solution 2 : 68ms

n = int(input())
def total_sum(n):
    t_sum = 0
    for i in range(n,0,-1):
        t_sum += i
    return t_sum
print(total_sum(n))