Problem:
Score : 200 points

Problem Statement

Square1001 has seen an electric bulletin board displaying the integer 1.
He can perform the following operations A and B to change this value:

Operation A: The displayed value is doubled.

Operation B: The displayed value increases by K.

Square1001 needs to perform these operations N times in total.
Find the minimum possible value displayed in the board after N operations.

Constraints

1 \leq N, K \leq 10

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
K

Output

Print the minimum possible value displayed in the board after N operations.

Sample Input 1

4
3

Sample Output 1

10

The value will be minimized when the operations are performed in the following order: A, A, B, B.

In this case, the value will change as follows: 1 → 2 → 4 → 7 → 10.

Sample Input 2

10
10

Sample Output 2

76

The value will be minimized when the operations are performed in the following order: A, A, A, A, B, B, B, B, B, B.

In this case, the value will change as follows: 1 → 2 → 4 → 8 → 16 → 26 → 36 → 46 → 56 → 66 → 76.

By the way, this contest is AtCoder Beginner Contest 076.

Solution in Ruby (2.3.3) (judge verdict: Accepted)

def a(c)
  c * 2
end

def b(c,k)
  c + k
end

n = gets.chomp.to_i
k = gets.chomp.to_i

op_a = lambda{|*args| a(*args)}
op_b = lambda{|*args| b(*args)}

c = 1
ans = []
arr = [op_a,op_b]
arr.repeated_permutation(n).each do |op|
  c = 1
  op.each do |o|
    if o == op_a
      c = o[c]
    else
      c = o[c,k]
    end
  end
  ans << c
end

puts ans.min