Hat's Fibonacci

 1 import java.lang.*;
 2 import java.util.*;
 3 import java.text.*;
 4 import java.math.*;
 5 import java.io.*;
 6 class Main
 7 {
 8     public static void main(String []args)
 9     {
10         int n,i;
11         BigInteger a1,a2,a3,a4,a5;
12         Scanner cin=new Scanner(System.in);
13         while(cin.hasNext())
14         {
15             a1=BigInteger.valueOf(1);
16             a2=BigInteger.valueOf(1);
17             a3=BigInteger.valueOf(1);
18             a4=BigInteger.valueOf(1);
19             a5=BigInteger.valueOf(1);
20             n=cin.nextInt();
21             for(i=5;i<=n;i++)
22             {
23                 a5=a4.add(a3.add(a2.add(a1)));
24                 a1=a2;
25                 a2=a3;
26                 a3=a4;
27                 a4=a5;
28             }
29             System.out.println(a5);
30         }
31     }
32 }
//也可以用数组，初始化可以省一些。