def first_non_repeating_character(str1):
  
  char_order = []
  ctr = {}
  for c in str1:
    if c in ctr:
      ctr[c] += 1
    else:
      ctr[c] = 1 
      char_order.append(c)
  for c in char_order:
    if ctr[c] == 1:
      return c
  return None
def first_non_repeating_character(str1):
    char_order = []
    ctr = {}
    for k in str1:
        if k in ctr:
            ctr[k] += 1
           
        else:
            ctr[k] = 1
            char_order.append(k)
    for k in char_order:
        if ctr[k] == 1:
            return k
    return None