递归

1,1,2,3,5,8,13,21,24......求第三十位

var y = sum(30);
            function sum(n){
            var s1=1
                if(n==1)
                    { 
                    s1=1;
                    }
                else if(n==2)
                    {
                    s1=1;
                    }
                else
                {
                s1 = sum(n-1) + sum(n-2);
                }
                return s1;
            }
            alert(y)