There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?
# -*- coding: utf-8 -*-


def main():
    """Function."""
    n = int(input())
    print((2*n + 1)*n//2)


if __name__ == "__main__":
    main()

# -*- coding: utf-8 -*-


def main():
    """Function."""
    n = int(input())
    print((n + 1)*n//2)


if __name__ == "__main__":
    main()
