import sys

dp=[0]*10001

for line in sys.stdin.readlines():

    n = int(line)

    dp[0]=1

    for i in range(1,n+1):

        dp[i]=dp[i-1]+i

    print(dp[n])
import sys

for line in sys.stdin.readlines():

    n = int(line)

    dp=1

    for i in range(1,n+1):

        dp+=i

    print(dp)
import sys

dp = [0] * 10001
for line in sys.stdin.readlines():
    n = int(line)
    dp[0] = 1
    for i in range(1, n + 1):
        dp[i] = dp[i - 1] + i
    print(dp[n])

import sys

for line in sys.stdin.readlines():
    n = int(line)
    dp = 1
    for i in range(1, n + 1):
        dp += i
    print(dp)

-dp = [0] * 10001 -    dp[0] = 1 +    dp = 1 -        dp[i] = dp[i - 1] + i -    print(dp[n]) +        dp += i +    print(dp)