6个一循环.....取模的时候很坑...

Jzzhu has invented a kind of sequences, they meet the following property:

You are given x and y, please calculate fn modulo 1000000007 (109?+?7).

The first line contains two integers x and y ("x|,?|y|?≤?109). The second line contains a single integer n (1?≤?n?≤?2?109).

Output a single integer representing fn modulo 1000000007 (109?+?7).

2 3
3

1

0 -1
2

1000000006

In the first sample, f2?=?f1?+?f3, 3?=?2?+?f3, f3?=?1.

In the second sample, f2?=??-?1; ?-?1 modulo (109?+?7) equals (109?+?6).

#include 
  
   
#include 
   
     #include 
    
      #include 
     
       using namespace std; typedef long long int LL; const LL mod=1000000007LL; LL a,b,n; int main() { cin>>a>>b>>n; n--; n=n%6; LL ans=0; switch(n) { case(0): { ans=(a+mod)%mod; break; } case(1): { ans=(b+mod)%mod; break; } case(2): { ans=(b-a+2*mod)%mod; break; } case(3): { ans=(mod-a)%mod; break; } case(4): { ans=(mod-b)%mod; break; } case(5): { ans=(a-b+2*mod)%mod; break; } } cout<