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: S = input()
  print("a:" + str(S.count("a")))
  print("b:" + str(S.count("b")))
  print("c:" + str(S.count("c")))
  print("d:" + str(S.count("d")))
  print("e:" + str(S.count("e")))
  print("f:" + str(S.count("f")))
  print("g:" + str(S.count("g")))
  print("h:" + str(S.count("h")))
  print("i:" + str(S.count("i")))
  print("j:" + str(S.count("j")))
  print("k:" + str(S.count("k")))
  print("l:" + str(S.count("l")))
  print("m:" + str(S.count("m")))
  print("n:" + str(S.count("n")))
  print("o:" + str(S.count("o")))
  print("p:" + str(S.count("p")))
  print("q:" + str(S.count("q")))
  print("r:" + str(S.count("r")))
  print("s:" + str(S.count("s")))
  print("t:" + str(S.count("t")))
  print("u:" + str(S.count("u")))
  print("v:" + str(S.count("v")))
  print("w:" + str(S.count("w")))
  print("x:" + str(S.count("x")))
  print("y:" + str(S.count("y")))
  print("z:" + str(S.count("z")))
  
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"}]