D-- Enumeration Structure Validator and Counter

D-- is a futuristic language from the year 2077. It introduces an "enumeration structure" which is represented by the following expression:

 X Y Z W 

In this expression:

• X and Z are single lowercase letters representing variable names.
• Y and W are integers representing the start and end values for enumeration.

For safety purposes, to successfully enumerate the variable X, it is required that Z is identical to X.

For example, a valid enumeration structure is:

 i 1 i 100 

This represents enumerating variable i from 1 to 100.

Your task is to process a given D-- enumeration expression X Y Z W and perform the following:

1. Check Validity: The expression is considered valid only if:
   • X and Z are lowercase letters.
   • X is equal to Z.
   • Y and W are integers. (You may assume this always holds in the given input.)
2. Count Enumeration Steps: If the expression is valid, compute the number of enumeration steps. If Y ≤ W, then the number of steps is W − Y + 1, otherwise it is Y − W + 1.

If the expression is invalid, output error.

inputFormat

The input consists of a single line containing four space-separated items: X Y Z W, where X and Z are letters and Y and W are integers.

outputFormat

If the expression is valid, output the number of steps the variable is enumerated across. Otherwise, output error.

sample

i 1 i 100

100