'To xor or not to xor sgu':http://acm.sgu.ru/problem.php?contest=0&problem=275
'Puzzle sgu':http://acm.sgu.ru/problem.php?contest=0&problem=260
'Rational Resistors uva':http://online-judge.uva.es/p/v108/10808.html
'Extrapolation Using a Difference Table uva':http://online-judge.uva.es/p/v3/326.html
'Simple calculations uva':http://online-judge.uva.es/p/v100/10014.html

'To xor or not to xor':http://acm.sgu.ru/problem.php?contest=0&problem=275
'Puzzle':http://acm.sgu.ru/problem.php?contest=0&problem=260
'Rational Resistors':http://online-judge.uva.es/p/v108/10808.html
'Extrapolation Using a Difference Table ':http://online-judge.uva.es/p/v3/326.html
'Simple calculations':http://online-judge.uva.es/p/v100/10014.html

'BColor infoarena':http://infoarena.ro/problema/bcolor

'Laser infoarena':http://infoarena.ro/problema/laser
'XORing topcoder':http://www.topcoder.com/stat?c=problem_statement&pm=4829&rd=8095&rm=246636&cr=270505
'Escape the jail topcoder':http://www.topcoder.com/stat?c=problem_statement&pm=7353

'Laser infoarena':http://infoarena.ro/problema/laser