#include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 #include <cmath>

 using namespace std;

 const int M = 1e5+;

 const int MOD = 1e9+;

 int x, y, n;

 int a[];

 int main()  {

     while( ~scanf("%d%d%d", &x, &y, &n ) )  {

         a[] = x;

         a[] = y;

         for( int i=; i<; i++ )    {

             if( i >=  )

                 a[i] = a[i-] - a[i-];

             while( a[i] <  )   {   //消除负数取mod的影响，将其转换成正数

                 a[i] += MOD;

             }

             a[i] %= MOD;

         }

         printf("%d\n", a[(n-)%] );

     }

     return ;

 }