n = int(input())  # 读取输入的整数 n
sum = 0  # 初始化累加和为 0
for i in range(1, n + 1):  # 从 1 到 n 逐个累加
    sum += i
print(sum)  # 输出结果
/**************************************************************
	Problem: 1002
	User: a99344
	Language: Python
	Result: Accepted
	Time:82 ms
	Memory:34244 kb
****************************************************************/