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An Arithmetic Problem

Limits: 1s, 512 MB

A sequence is an arithmetic sequence if every two successive number has same difference. Suppose this is a sequence of numbers:

a1, a2, a3,………………

This is an arithmetic sequence if ai-ai+1 is same for each i from 1 to n-1.

You are given first 3 terms of a sequence and the value of n. If it is an arithmetic sequence you must print the nth term. Otherwise you must print “Error”.


In First line there will be an integer T denoting number of test cases. Each of the case will contain 4 integers a1, a2, a3 and n.


  • 1 ≤ T ≤ 100
  • -300 ≤ a1, a2, a3 ≤ 300
  • 1 ≤ n ≤ 1000


In each line specify the case number and print the answer.


1 2 3 10
1 4 3 10
15 30 45 5
Case 1: 10
Case 2: Error
Case 3: 75


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