according to the digit 's position,  obtain the last digit of the  applicable perfect power of 2
if ( posFromRight % 4 == 1 ) : NEW_LINE INDENT sum = sum + 2 NEW_LINE DEDENT elif ( posFromRight % 4 == 2 ) : NEW_LINE INDENT sum = sum + 4 NEW_LINE DEDENT elif ( posFromRight % 4 == 3 ) : NEW_LINE INDENT sum = sum + 8 NEW_LINE DEDENT elif ( posFromRight % 4 == 0 ) : NEW_LINE INDENT sum = sum + 6 NEW_LINE DEDENT