2014/7/19 codeforces div2 B

http://codeforces.com/contest/450/problem/B

#include<iostream>
#include<cstdlib>
#include<cstdlib>
using namespace std;
typedef long long LL;
const long long mod=1000000007;
int main(){
    LL a[4];
    LL x,y;
    LL n,ans;
    while(cin>>x>>y>>n){
    a[1]=x;a[2]=y;a[0]=y-x;
       LL ch=n/3;
       LL mo=n%3;
       if(mo)
        ch++;
        ans=a[mo]%mod;
        if(ch%2==0)
        ans*=-1;
        while(ans<0)
        ans+=mod;
        cout<<ans%mod<<endl;
    }
    return 0;
}