Discrete mathematics, will rate :)

20. (5 points) Given the following algorithm: If n=0, then f(n)=0 else if n=1, then f(n)=1 else f(n)=f(n1)+f(n2). For n0, let c(n) be the total number of additions for calculating f(n)( Hint: c(0)=0,c(1)=0,c(2)=1). For n2 express c(n) using c(n1) and c(n2)