# Put 1 grain of rice on the first square of a chess board, 2 on the second
# 4 on the third, 8 on the fourth, and so forth. Find how many grains of rice
# are on the board after you get to n squares
#
# Matt Bishop, MHI 289I, Winter 2019
#

try:
    n = int(input("Number of squares? "))
except:
    print("Need a positive integer!")
else:
    # sanity check input
    if n < 1:
        print("Your integer must be positive!")
    else:
        # good to go!
        # total = number of grains of rice on board
        # as n is at least 1, there will be at least
        # 1 grain of rice
        total = 1
        # x = number of grains of rice on current square
        x = 1
        # now add up the rice grains
        for i in range(1, n):
            # going to the next square, so we double the
            # number of grains of rice on the previous
            # square to get the number on the current square
            x = 2 * x
            # now add it into the total
            total = total + x
        # done! print it out
        print("On a chessboard of", n, "squares, there are", total, "grains of rice")