
# 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



read = sys.stdin.read

readline = sys.stdin.readline

readlines = sys.stdin.readlines

sys.setrecursionlimit(10 ** 9)

INF = 1 << 60





def main():

    N, K, *A = list(map(int, read().split()))



    ans = INF

    for bit in range(1 << N):

        if (not (bit & 1)) or bin(bit).count('1') != K:

            continue



        total = 0

        max_height = A[0]

        for i, a in enumerate(A[1:], 1):

            if a <= max_height:

                if bit & (1 << i):

                    total += max_height - a + 1

                    max_height += 1

            else:

                max_height = a



        if ans > total:

            ans = total



    print(ans)



    return





if __name__ == '__main__':

    main()


# optimized version of the same code:

import sys

from itertools import combinations



read = sys.stdin.read

readline = sys.stdin.readline

readlines = sys.stdin.readlines

sys.setrecursionlimit(10 ** 9)

INF = 1 << 60





def main():

    N, K, *A = list(map(int, read().split()))



    ans = INF

    for comb in combinations(list(range(1, N)), K - 1):

        included = [False] * N

        for i in comb:

            included[i] = True



        total = 0

        max_height = A[0]

        for i, a in enumerate(A[1:], 1):

            if a <= max_height:

                if included[i]:

                    total += max_height - a + 1

                    max_height += 1

            else:

                max_height = a



        if ans > total:

            ans = total



    print(ans)



    return





if __name__ == '__main__':

    main()

import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10**9)
INF = 1 << 60


def main():
    N, K, *A = list(map(int, read().split()))
    ans = INF
    for bit in range(1 << N):
        if (not (bit & 1)) or bin(bit).count("1") != K:
            continue
        total = 0
        max_height = A[0]
        for i, a in enumerate(A[1:], 1):
            if a <= max_height:
                if bit & (1 << i):
                    total += max_height - a + 1
                    max_height += 1
            else:
                max_height = a
        if ans > total:
            ans = total
    print(ans)
    return


if __name__ == "__main__":
    main()

import sys
from itertools import combinations

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10**9)
INF = 1 << 60


def main():
    N, K, *A = list(map(int, read().split()))
    ans = INF
    for comb in combinations(list(range(1, N)), K - 1):
        included = [False] * N
        for i in comb:
            included[i] = True
        total = 0
        max_height = A[0]
        for i, a in enumerate(A[1:], 1):
            if a <= max_height:
                if included[i]:
                    total += max_height - a + 1
                    max_height += 1
            else:
                max_height = a
        if ans > total:
            ans = total
    print(ans)
    return


if __name__ == "__main__":
    main()

+from itertools import combinations -    for bit in range(1 << N): -        if (not (bit & 1)) or bin(bit).count("1") != K: -            continue +    for comb in combinations(list(range(1, N)), K - 1): +        included = [False] * N +        for i in comb: +            included[i] = True -                if bit & (1 << i): +                if included[i]: