1001

http://acm.hdu.edu.cn/showproblem.php?pid=1001

题目要求：输入一个整数n，从1开始，一到n，数字相加求和

i = 1
s = 0
n = float(input())
n1 = n +1
while i< n1:
   s = s + i
   i = i + 1
print(s)