
# 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:

while int(eval(input())) > 0:

    s = sorted(map(int, input().split()))

    print((min(abs(a - b) for (a, b) in zip(s, s[1:]))))

# optimized version of the same code:

while True:

    if int(eval(input())) == 0:

        break

    s = sorted(map(int, input().split()))

    r = min(abs(x - y) for (x, y) in zip(s, s[1:]))

    print(r)
while int(eval(input())) > 0:
    s = sorted(map(int, input().split()))
    print((min(abs(a - b) for (a, b) in zip(s, s[1:]))))

while True:
    if int(eval(input())) == 0:
        break
    s = sorted(map(int, input().split()))
    r = min(abs(x - y) for (x, y) in zip(s, s[1:]))
    print(r)

-while int(eval(input())) > 0: +while True: +    if int(eval(input())) == 0: +        break -    print((min(abs(a - b) for (a, b) in zip(s, s[1:])))) +    r = min(abs(x - y) for (x, y) in zip(s, s[1:])) +    print(r)