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: # coding: UTF-8
  
  buf = str(input())
  
  print("a :", buf.count("a") + buf.count("A"))
  print("b :", buf.count("b") + buf.count("B"))
  print("c :", buf.count("c") + buf.count("C"))
  print("d :", buf.count("d") + buf.count("D"))
  print("e :", buf.count("e") + buf.count("E"))
  print("f :", buf.count("f") + buf.count("F"))
  print("g :", buf.count("g") + buf.count("G"))
  print("h :", buf.count("h") + buf.count("H"))
  print("i :", buf.count("i") + buf.count("I"))
  print("j :", buf.count("j") + buf.count("J"))
  print("k :", buf.count("k") + buf.count("K"))
  print("l :", buf.count("l") + buf.count("L"))
  print("m :", buf.count("m") + buf.count("M"))
  print("n :", buf.count("n") + buf.count("N"))
  print("o :", buf.count("o") + buf.count("O"))
  print("p :", buf.count("p") + buf.count("P"))
  print("q :", buf.count("q") + buf.count("Q"))
  print("r :", buf.count("r") + buf.count("R"))
  print("s :", buf.count("s") + buf.count("S"))
  print("t :", buf.count("t") + buf.count("T"))
  print("u :", buf.count("u") + buf.count("U"))
  print("v :", buf.count("v") + buf.count("V"))
  print("w :", buf.count("w") + buf.count("W"))
  print("x :", buf.count("x") + buf.count("X"))
  print("y :", buf.count("y") + buf.count("Y"))
  print("z :", buf.count("z") + buf.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"}]