# fibonacci number;


fib(n_,x_) := if(n==0,0, If(n==1,1, if(n==2,x, if(abs(n)>2,fib(abs(n)-1)+fib(abs(n)-2)*x ))));
fib(n_) := if(n==0,0,If(abs(n)<3,1, if(abs(n)>2,(fib(abs(n)-1)+fib(abs(n)-2)) )));