
# slower version:

s = input()
for i in range(len(s)):
  if i%2 == 0:
    print(s[i], end = '')


# optimized version of the same code:

s = input()
ans = ''
for i in range(len(s)):
  if i % 2 == 0:
    ans += s[i]
print(ans)



# slower version:

n = int(eval(input()))

leaves = list(map(int, input().split()))



ans = 0

nodes_min = [0] * (n + 1)

nodes_max = [0] * (n + 1)

nodes_min[n] = leaves[n]

nodes_max[n] = leaves[n]



for depth in range(n, 0, -1):

    root_min = nodes_min[depth] // 2 + nodes_min[depth] % 2

    nodes_min[depth - 1] = leaves[depth - 1] + root_min

    root_max = nodes_max[depth]

    nodes_max[depth - 1] = leaves[depth - 1] + root_max

nodes = [0] * (n + 1)

nodes[0] = 1

if nodes[0] < nodes_min[0]:

    print((-1))

else:

    for depth in range(n):

        roots = nodes[depth]-leaves[depth]

        nodes[depth + 1] = min(roots * 2, nodes_max[depth + 1])

        if nodes[depth+1] < nodes_min[depth+1]:

            print((-1))

            break

    else:

        print((sum(nodes)))


# optimized version of the same code:

n = int(eval(input()))

leaves = list(map(int, input().split()))



sum_leaves = [0]*(n+1)

sum_leaves[0] = leaves[0]

for depth in range(n):

    sum_leaves[depth+1] = sum_leaves[depth] + leaves[depth+1]



ans = 0



root = [None] * (n + 1)

if n == 0:

    root[0] = 0

else:

    root[0] = 1

if root[0] + leaves[0] != 1:

    print((-1))

else:

    for depth in range(n):

        root[depth+1] = min(2*root[depth]-leaves[depth+1],

                            sum_leaves[n]-sum_leaves[depth+1])

        if root[depth + 1] < root[depth] - leaves[depth + 1] or root[depth+1] < 0:

            print((-1))

            break

    else:

        print((sum(root)+sum(leaves)))

n = int(eval(input()))
leaves = list(map(int, input().split()))
ans = 0
nodes_min = [0] * (n + 1)
nodes_max = [0] * (n + 1)
nodes_min[n] = leaves[n]
nodes_max[n] = leaves[n]
for depth in range(n, 0, -1):
    root_min = nodes_min[depth] // 2 + nodes_min[depth] % 2
    nodes_min[depth - 1] = leaves[depth - 1] + root_min
    root_max = nodes_max[depth]
    nodes_max[depth - 1] = leaves[depth - 1] + root_max
nodes = [0] * (n + 1)
nodes[0] = 1
if nodes[0] < nodes_min[0]:
    print((-1))
else:
    for depth in range(n):
        roots = nodes[depth] - leaves[depth]
        nodes[depth + 1] = min(roots * 2, nodes_max[depth + 1])
        if nodes[depth + 1] < nodes_min[depth + 1]:
            print((-1))
            break
    else:
        print((sum(nodes)))

n = int(eval(input()))
leaves = list(map(int, input().split()))
sum_leaves = [0] * (n + 1)
sum_leaves[0] = leaves[0]
for depth in range(n):
    sum_leaves[depth + 1] = sum_leaves[depth] + leaves[depth + 1]
ans = 0
root = [None] * (n + 1)
if n == 0:
    root[0] = 0
else:
    root[0] = 1
if root[0] + leaves[0] != 1:
    print((-1))
else:
    for depth in range(n):
        root[depth + 1] = min(
            2 * root[depth] - leaves[depth + 1], sum_leaves[n] - sum_leaves[depth + 1]
        )
        if root[depth + 1] < root[depth] - leaves[depth + 1] or root[depth + 1] < 0:
            print((-1))
            break
    else:
        print((sum(root) + sum(leaves)))

+sum_leaves = [0] * (n + 1) +sum_leaves[0] = leaves[0] +for depth in range(n): +    sum_leaves[depth + 1] = sum_leaves[depth] + leaves[depth + 1] -nodes_min = [0] * (n + 1) -nodes_max = [0] * (n + 1) -nodes_min[n] = leaves[n] -nodes_max[n] = leaves[n] -for depth in range(n, 0, -1): -    root_min = nodes_min[depth] // 2 + nodes_min[depth] % 2 -    nodes_min[depth - 1] = leaves[depth - 1] + root_min -    root_max = nodes_max[depth] -    nodes_max[depth - 1] = leaves[depth - 1] + root_max -nodes = [0] * (n + 1) -nodes[0] = 1 -if nodes[0] < nodes_min[0]: +root = [None] * (n + 1) +if n == 0: +    root[0] = 0 +else: +    root[0] = 1 +if root[0] + leaves[0] != 1: -        roots = nodes[depth] - leaves[depth] -        nodes[depth + 1] = min(roots * 2, nodes_max[depth + 1]) -        if nodes[depth + 1] < nodes_min[depth + 1]: +        root[depth + 1] = min( +            2 * root[depth] - leaves[depth + 1], sum_leaves[n] - sum_leaves[depth + 1] +        ) +        if root[depth + 1] < root[depth] - leaves[depth + 1] or root[depth + 1] < 0: -        print((sum(nodes))) +        print((sum(root) + sum(leaves)))