Help with string

Rahul ha been given a string containing space separated integers. He does not know how many integers are in the string. He has also been given 2 integers a,b. He has to make a fibonacci type of sequence with it. i.e nth term is sum of (n-1)th term and (n-2)th term. Finally he has to calculate the sum of the nth integer in the above sequence for every integer n in the string. As the output can