#coding : utf-8

x = int(input().rstrip())

ans = 0
for i in range(1,x+1):
    ans += i

print(ans)



# <?php

#     $x = trim(fgets(STDIN));
    
#     $ans = 0;
#     for($i = 1; $i <= $x; $i++) {
#         $ans += $i;
#     }
    
#     echo $ans;

# ?>