IKMC 2012 - Grades 11-12 - Paper 02 - Self-study Question 29

The sequence starts 1, 1, 0, 1, −1, … . Its first two terms are a₁ = a₂ = 1. Then a₃ = a₁ − a₂, a₄ = a₂ + a₃, a₅ = a₃ − a₄, a₆ = a₄ + a₅, and so on, alternating difference and sum. What is the sum of the first 100 terms?