
# 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

input = sys.stdin.readline

input = sys.stdin.buffer.readline





def RD(): return sys.stdin.read()

def II(): return int(eval(input()))

def MI(): return list(map(int,input().split()))

def LI(): return list(map(int,input().split()))

def TI(): return tuple(map(int,input().split()))



# mod=10**9+7

# rstrip().decode('utf-8')



import numpy as np

from itertools import combinations



def main():

	n,k=MI()

	ans=10**18



	A=LI()

	A=[A[0]-1]+A

	A=np.array(A)



	for t in combinations(list(range(n)),k):

		B=A.copy()

		tmp=0

		for i in t:

			i+=1

			B[i]=max(B[:i].max()+1,A[i])

			tmp+=B[i]-A[i]

		ans=min(ans,tmp)

	print(ans)



if __name__ == "__main__":

	main()


# optimized version of the same code:

import sys

input = sys.stdin.readline

input = sys.stdin.buffer.readline





def RD(): return sys.stdin.read()

def II(): return int(eval(input()))

def MI(): return list(map(int,input().split()))

def LI(): return list(map(int,input().split()))

def TI(): return tuple(map(int,input().split()))



# mod=10**9+7

# rstrip().decode('utf-8')



#import numpy as np

from itertools import combinations



def main():

	n,k=MI()

	ans=10**18



	A=LI()

	A=[A[0]-1]+A



	for t in combinations(list(range(n)),k):

		B=A.copy()

		tmp=0

		for i in t:

			i+=1

			B[i]=max(max(B[:i])+1,A[i])

			tmp+=B[i]-A[i]

		ans=min(ans,tmp)

	print(ans)



if __name__ == "__main__":

	main()

import sys

input = sys.stdin.readline
input = sys.stdin.buffer.readline


def RD():
    return sys.stdin.read()


def II():
    return int(eval(input()))


def MI():
    return list(map(int, input().split()))


def LI():
    return list(map(int, input().split()))


def TI():
    return tuple(map(int, input().split()))


# mod=10**9+7
# rstrip().decode('utf-8')
import numpy as np
from itertools import combinations


def main():
    n, k = MI()
    ans = 10**18
    A = LI()
    A = [A[0] - 1] + A
    A = np.array(A)
    for t in combinations(list(range(n)), k):
        B = A.copy()
        tmp = 0
        for i in t:
            i += 1
            B[i] = max(B[:i].max() + 1, A[i])
            tmp += B[i] - A[i]
        ans = min(ans, tmp)
    print(ans)


if __name__ == "__main__":
    main()

import sys

input = sys.stdin.readline
input = sys.stdin.buffer.readline


def RD():
    return sys.stdin.read()


def II():
    return int(eval(input()))


def MI():
    return list(map(int, input().split()))


def LI():
    return list(map(int, input().split()))


def TI():
    return tuple(map(int, input().split()))


# mod=10**9+7
# rstrip().decode('utf-8')
# import numpy as np
from itertools import combinations


def main():
    n, k = MI()
    ans = 10**18
    A = LI()
    A = [A[0] - 1] + A
    for t in combinations(list(range(n)), k):
        B = A.copy()
        tmp = 0
        for i in t:
            i += 1
            B[i] = max(max(B[:i]) + 1, A[i])
            tmp += B[i] - A[i]
        ans = min(ans, tmp)
    print(ans)


if __name__ == "__main__":
    main()

-import numpy as np +# import numpy as np -    A = np.array(A) -            B[i] = max(B[:i].max() + 1, A[i]) +            B[i] = max(max(B[:i]) + 1, A[i])