output_description: Prints the number of alphabetical letters in the following format:
  
      
      
      a : _The number of 'a'_
      b : _The number of 'b'_
      c : _The number of 'c'_
        .
        .
      z : _The number of 'z'_
input_description: A sentence in English is given in several lines.
attempt: a = [0] * 26
  w = "abcdefghijklmnopqrstuvwxyz"
  s = list(input().upper())
  for i in s:
      if i == "A":
          a[0] += 1
      elif i == "B":
          a[1] += 1
      elif i == "C":
          a[2] += 1
      elif i == "D":
          a[3] += 1
      elif i == "E":
          a[4] += 1
      elif i == "F":
          a[5] += 1
      elif i == "G":
          a[6] += 1
      elif i == "H":
          a[7] += 1
      elif i == "I":
          a[8] += 1
      elif i == "J":
          a[9] += 1
      elif i == "K":
          a[10] += 1
      elif i == "L":
          a[11] += 1
      elif i == "M":
          a[12] += 1
      elif i == "N":
          a[13] += 1
      elif i == "O":
          a[14] += 1
      elif i == "P":
          a[15] += 1
      elif i == "Q":
          a[16] += 1
      elif i == "R":
          a[17] += 1
      elif i == "S":
          a[18] += 1
      elif i == "T":
          a[19] += 1
      elif i == "U":
          a[20] += 1
      elif i == "V":
          a[21] += 1
      elif i == "W":
          a[22] += 1
      elif i == "X":
          a[23] += 1
      elif i == "Y":
          a[24] += 1
      elif i == "Z":
          a[25] += 1
  for i in range(26):
      print(w[i : i + 1], ":", str(a[i]))
  
problem_description: Counting Characters
  
    
  
  Write a program which counts and reports the number of each alphabetical
  letter. Ignore the case of characters.
samples: [{"input": "This is a pen.", "output": "a : 1\n    b : 0\n    c : 0\n    d : 0\n    e : 1\n    f : 0\n    g : 0\n    h : 1\n    i : 2\n    j : 0\n    k : 0\n    l : 0\n    m : 0\n    n : 1\n    o : 0\n    p : 1\n    q : 0\n    r : 0\n    s : 2\n    t : 1\n    u : 0\n    v : 0\n    w : 0\n    x : 0\n    y : 0\n    z : 0"}]