output_description: Print the formula you made, including the part `=7`.
  
  Use the signs `+` and `-`.
  
  Do not print a space between a digit and a sign.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      ABCD
attempt: def check(operate_list, num_list):
      res = num_list[0]
      for i, op in enumerate(operate_list):
          if op == "+":
              res += num_list[i+1]
          elif op == "-":
              res -= num_list[i+1]
      return res == 7
  
  def concat(operate_list, num_list):
      string = num_list[0]
      for op, num in zip(operate_list, num_list[1:]):
          # it is beautiful!
          string += op
          string =+ num
      string += "="
      return string
  
  def main():
      line = sys.stdin.readline().strip()
      num_list = []
      for s in line:
          num_list.append(int(s))
      result = ""
      stack = []
      stack.append([])
      N = len(num_list)
      while(len(stack) != 0){
          l = stack.pop()
          if len(l) == N-1:
              if check(l, num_list):
                  result = concat(l, num_list)
                  break
          else:
              stack.append(l + ["+"]) # careful code
              stack.append(l + ["-"])
      }
      print(result)
  
problem_description: Statement
  
  Sitting in a station waiting room, Joisino is gazing at her train ticket.
  
  The ticket is numbered with four digits A, B, C and D in this order, each
  between 0 and 9 (inclusive).
  
  In the formula A op1 B op2 C op3 D = 7, replace each of the symbols op1, op2
  and op3 with `+` or `-` so that the formula holds.
  
  The given input guarantees that there is a solution. If there are multiple
  solutions, any of them will be accepted.
samples: [{"input": "1222", "output": "1+2+2+2=7\n    \n\nThis is the only valid solution.\n\n* * *"}, {"input": "0290", "output": "0-2+9+0=7\n    \n\n0 - 2 + 9 - 0 = 7 is also a valid solution.\n\n* * *"}, {"input": "3242", "output": "3+2+4-2=7"}]