
# 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:

import sys

import numpy as np



N, M = [int(_) for _ in input().split()]



if M == 0:

    if N == 1:

        print("0")

    else:

        ans = [0] * N

        ans[0] = 1

        print(("".join(map(str, ans))))

    sys.exit()



S, C = np.array([[int(_) for _ in input().split()] for i in range(M)]).T



ans = [-1] * N



for i in range(M):

    j = int(S[i]) - 1

    if ans[j] == -1 or ans[j] == C[i]:

        ans[j] = C[i]

    else:

        print("-1")

        sys.exit()



if N >= 2 and ans[0] == 0:

    print("-1")

    sys.exit()



if N >= 2 and ans[0] == -1:

    ans[0] = 1



for i in range(1, N):

    if ans[i] == -1:

        ans[i] = 0



s = "".join(map(str, ans))

print(s)


# optimized version of the same code:

import sys



N, M = [int(_) for _ in input().split()]

SC = [[int(_) for _ in input().split()] for i in range(M)]



if N == 1:

    start = 0

    end = 10

else:

    start = 10 ** (N - 1)

    end = 10 ** N



for i in range(start, end):

    ans = list(map(int, str(i)))

    valid = True

    for s, c in SC:

        if ans[s-1] != c:

            valid = False

            break

    if valid:

        print(i)

        sys.exit()



print((-1))

import sys
import numpy as np

N, M = [int(_) for _ in input().split()]
if M == 0:
    if N == 1:
        print("0")
    else:
        ans = [0] * N
        ans[0] = 1
        print(("".join(map(str, ans))))
    sys.exit()
S, C = np.array([[int(_) for _ in input().split()] for i in range(M)]).T
ans = [-1] * N
for i in range(M):
    j = int(S[i]) - 1
    if ans[j] == -1 or ans[j] == C[i]:
        ans[j] = C[i]
    else:
        print("-1")
        sys.exit()
if N >= 2 and ans[0] == 0:
    print("-1")
    sys.exit()
if N >= 2 and ans[0] == -1:
    ans[0] = 1
for i in range(1, N):
    if ans[i] == -1:
        ans[i] = 0
s = "".join(map(str, ans))
print(s)

import sys

N, M = [int(_) for _ in input().split()]
SC = [[int(_) for _ in input().split()] for i in range(M)]
if N == 1:
    start = 0
    end = 10
else:
    start = 10 ** (N - 1)
    end = 10**N
for i in range(start, end):
    ans = list(map(int, str(i)))
    valid = True
    for s, c in SC:
        if ans[s - 1] != c:
            valid = False
            break
    if valid:
        print(i)
        sys.exit()
print((-1))

-import numpy as np -if M == 0: -    if N == 1: -        print("0") -    else: -        ans = [0] * N -        ans[0] = 1 -        print(("".join(map(str, ans)))) -    sys.exit() -S, C = np.array([[int(_) for _ in input().split()] for i in range(M)]).T -ans = [-1] * N -for i in range(M): -    j = int(S[i]) - 1 -    if ans[j] == -1 or ans[j] == C[i]: -        ans[j] = C[i] -    else: -        print("-1") +SC = [[int(_) for _ in input().split()] for i in range(M)] +if N == 1: +    start = 0 +    end = 10 +else: +    start = 10 ** (N - 1) +    end = 10**N +for i in range(start, end): +    ans = list(map(int, str(i))) +    valid = True +    for s, c in SC: +        if ans[s - 1] != c: +            valid = False +            break +    if valid: +        print(i) -if N >= 2 and ans[0] == 0: -    print("-1") -    sys.exit() -if N >= 2 and ans[0] == -1: -    ans[0] = 1 -for i in range(1, N): -    if ans[i] == -1: -        ans[i] = 0 -s = "".join(map(str, ans)) -print(s) +print((-1))