class zigzagconv:
  def convert(self,s,numrows):
    firstcalcfactor =self.calcadditionfactor(numrows)
    difffactor = []
    if(numrows == 0):
      print ('')
      return ''
    if(numrows==1):
      print(s)
      return(s)

    if(s != '' and numrows !=0):
      for row in range(numrows,0,-1):
        if(row ==1 or row==numrows):
          difffactor.append(firstcalcfactor)
        else:
          difffactor.append(self.calcadditionfactor(row))
      #print(difffactor)
      strarr=[]
      for i in range(0,len(s)+firstcalcfactor+1,firstcalcfactor+1):
        #print(strarr)
        if(i == 0):
          afrarr = []
          afrarr.append(s[i])
          strarr.append(afrarr)
        else:
          if(i <len(s)):
            strarr[0].append(s[i])
        for row in range(1,numrows-1):
          if(i == 0):
            afrarr2 = []
            if((i+row)<len(s)):
              afrarr2.append(s[i+row])
            if(i+row+difffactor[row]+1<len(s)):
              afrarr2.append(s[i+row+difffactor[row]+1])
            if(len(afrarr2)>0):
              strarr.append(afrarr2)
          else:
            if((i+row)<len(s)):
              strarr[row].append(s[i+row])
            if(i+row+difffactor[row]+1<len(s)):
              strarr[row].append(s[i+row+difffactor[row]+1])

        if(i == 0):
          afrarr = []
          afrarr.append(s[i+numrows-1])
          strarr.append(afrarr)
        else:
          if(i+numrows-1<len(s)):
            strarr[numrows-1].append(s[i+numrows-1])
      finalstring =''

      for i in range(numrows):
        finalstring=finalstring+ (''.join(strarr[i]))
      print(finalstring)
      return finalstring
    else:
      print('')
      return ''

  def calcadditionfactor(self,numrows):
    return (numrows-1)*2-1

def inputfunc():
  ip1 = input()
  ip2 = input()
  ip3 = input()
  return (ip1, ip2 ,ip3);

def processingfunc(ip1,ip2,ip3):
  #Write code for the problem here

  return (ip1,ip2,ip3)

def main():
  # ip1,ip2,ip3 =inputfunc()
  # op1,op2,op3 = processingfunc(ip1,ip2,ip3)
  # if(op1 != None or op1  != ''):
  #   print(op1)
  # if(op2 != None or op2  != ''):
  #   print(op3)
  # if(op3 != None or op3  != ''):
  #   print(op3)
  zisk = zigzagconv()
  zisk.convert("PAYPALISHIRING",4)

main()