
# 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()))

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

n = N % 2



DP = [[0] * (N+1) for _ in range(N+1)]



for w in range(1, N+1):

    for i in range(N):

        j = i + w

        if j > N:

            continue

        if (w+n) % 2 == 1:

            DP[i][j] = min(DP[i+1][j] - A[i], DP[i][j-1] - A[j-1])

        else:

            DP[i][j] = max(DP[i+1][j] + A[i], DP[i][j-1] + A[j-1])



print((DP[0][N]))


# optimized version of the same code:

N = int(eval(input()))

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

DP = [[0] * (N+1) for _ in range(N+1)]



for num in range(1, N + 1):

    for start in range(N):

        end = start + num

        if end > N:

            break

        if num == 1:

            DP[start][end] = A[start]

        else:

            DP[start][end] = max(A[start] - DP[start+1][end], A[end - 1] - DP[start][end - 1])

print((DP[0][N]))

N = int(eval(input()))
A = list(map(int, input().split()))
n = N % 2
DP = [[0] * (N + 1) for _ in range(N + 1)]
for w in range(1, N + 1):
    for i in range(N):
        j = i + w
        if j > N:
            continue
        if (w + n) % 2 == 1:
            DP[i][j] = min(DP[i + 1][j] - A[i], DP[i][j - 1] - A[j - 1])
        else:
            DP[i][j] = max(DP[i + 1][j] + A[i], DP[i][j - 1] + A[j - 1])
print((DP[0][N]))

N = int(eval(input()))
A = list(map(int, input().split()))
DP = [[0] * (N + 1) for _ in range(N + 1)]
for num in range(1, N + 1):
    for start in range(N):
        end = start + num
        if end > N:
            break
        if num == 1:
            DP[start][end] = A[start]
        else:
            DP[start][end] = max(
                A[start] - DP[start + 1][end], A[end - 1] - DP[start][end - 1]
            )
print((DP[0][N]))

-n = N % 2 -for w in range(1, N + 1): -    for i in range(N): -        j = i + w -        if j > N: -            continue -        if (w + n) % 2 == 1: -            DP[i][j] = min(DP[i + 1][j] - A[i], DP[i][j - 1] - A[j - 1]) +for num in range(1, N + 1): +    for start in range(N): +        end = start + num +        if end > N: +            break +        if num == 1: +            DP[start][end] = A[start] -            DP[i][j] = max(DP[i + 1][j] + A[i], DP[i][j - 1] + A[j - 1]) +            DP[start][end] = max( +                A[start] - DP[start + 1][end], A[end - 1] - DP[start][end - 1] +            )