递归--1 ，2,3,5,8----

public class MainClass
{
public static void Main()
{
console.WriteLine(Foo(30));
}

public static intFoo(int i)
{
 if(i<=0)
return 0;
else if(i>1 && i<=2)
return 1;
else return Foo(i-1)+Foo(i+2)
}
}