题解 | #等差数列#
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
while True:
try:
n = int(input())
result = 0
next_num = 2
for i in range(1, n + 1):
result += next_num
next_num += 3
print(result)
except:
break
