Farmer Feb

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Farmer Feb has three fields with potatoes planted in them. He harvested x potatoes from the first field, y potatoes from the second field and is yet to harvest potatoes from the third field. Feb is very superstitious and believes that if the sum of potatoes he harvests from the three fields is a prime number (http://en.wikipedia.org/wiki/Prime_number), he'll make a huge profit. Please help him by calculating for him the minimum number of potatoes that if harvested from the third field will make the sum of potatoes prime. At least one potato should be harvested from the third field.
Input
The first line of the input contains an integer T denoting the number of test cases. Each of the next T lines contain 2 integers separated by single space: x and y.
Output
For each test case, output a single line containing the answer.
Constraints
 1 ≤ T ≤ 1000
 1 ≤ x ≤ 1000
 1 ≤ y ≤ 1000
Example
Input: 2 1 3 4 3 Output: 1 4
Explanation
In example case 1: the farmer harvested a potato from the first field and 3 potatoes from the second field. The sum is 4. If he is able to harvest a potato from the third field, that will make the sum 5, which is prime. Hence the answer is 1(he needs one more potato to make the sum of harvested potatoes prime.)
Author:  mischievous_me 
Tester:  shiplu 
Editorial  http://discuss.codechef.com/problems/POTATOES 
Tags  adhoc april14 cakewalk mischievous_me 
Date Added:  5012014 
Time Limit:  3 sec 
Source Limit:  50000 Bytes 
Languages:  ADA, ASM, BASH, BF, C, C99 strict, CAML, CLOJ, CLPS, CPP 4.3.2, CPP 4.9.2, CPP14, CS2, D, ERL, FORT, FS, GO, HASK, ICK, ICON, JAVA, JS, LISP clisp, LISP sbcl, LUA, NEM, NICE, NODEJS, PAS fpc, PAS gpc, PERL, PERL6, PHP, PIKE, PRLG, PYTH, PYTH 3.4, RUBY, SCALA, SCM guile, SCM qobi, ST, TCL, TEXT, WSPC 
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this is really good!
:) Nice Question.
How do I know the test cases
VICTORIOUS hahahahahahaahaha
AC in second attempt, used
i am not able to understand
conquer it ... feeling happy
my output for every input is
why we are finding the answer