Find the Missing Letter

You are given a sequence of consecutive (increasing) characters with exactly one missing letter in the sequence. Your task is to identify and output the missing letter. If there is no missing letter, output an empty string.

For example, given the sequence 'a b c d f', the missing letter is 'e', because the letters should follow consecutive order: a, b, c, d, e, f.

The expected input consists of a single line containing the characters separated by spaces. The output is the missing letter if found, or an empty string otherwise.

The relation between consecutive letters can be expressed using the Unicode code value: if \(a_1, a_2\) are two consecutive characters, they must satisfy \(\text{ord}(a_2)=\text{ord}(a_1)+1\). If not, then \(a_1+1\) is the missing letter.

inputFormat

The input is read from standard input (stdin) and consists of a single line containing a sequence of space-separated characters. Each character is an uppercase or lowercase English letter.

Example: a b c d f

outputFormat

The output is written to standard output (stdout). It should be the missing letter in the sequence. If no letter is missing, output an empty string.

Example: for the input a b c d f, the output is e.

a b c d f

e