Write a C program to read a string from the user and check whether the string is a pangram or not.

A pangram is a sentence containing every letter in the English alphabet. If the sentence is not a pangram print the alphabets that are missing that will make the sentence a pangram.

For example, the sentence, The quick brown fox jumps over the lazy dog is a pangram as it contains all the characters from a to z. The sentence The quick brown fox jumps over the dog is not a pangram because the characters a, l, z and y are missing.