#include<iostream>

 #include<cstdio>

 #include<cstring>

 using namespace std;

 #define ll long long

 const int maxn = ;

 const ll mod = 1e9+;

 ll n,p;

 struct Matrix{

     ll a[maxn][maxn];

     void init(){

         memset(a, , sizeof(a));

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

             a[i][i] = ;

         }

     }

 };

 //矩阵乘法

 Matrix mul(Matrix a, Matrix b){

     Matrix ans;

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

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

             ans.a[i][j] = ;

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

                 ans.a[i][j] = ans.a[i][j] % mod + a.a[i][k] * b.a[k][j] % mod;

                 ans.a[i][j] %= mod;

             }

         }

     }

     return ans;

 }

 //矩阵快速幂

 Matrix qpow(Matrix a,ll b){

     Matrix ans;

     ans.init();

     while(b){

         if(b & )

             ans = mul(ans,a);

         a = mul(a,a);

         b >>= ;

     }

     return ans;

 }

 void print(Matrix a){

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

         for(int j = ;j <= n;++j){

             cout << a.a[i][j]%mod<< " ";

         }

         cout << endl;

     }

 }

 int main(){

     Matrix base;

     Matrix ans;

     int x,y,n;

     cin>>x>>y>>n;

     if(n == ){

         cout<<(mod + x) % mod<<endl;

         return ;

     }

     if( n == ){

         cout<<(mod + y) % mod<<endl;

         return ;

     }

     ans.a[][] = y;ans.a[][] = x;

     base.a[][] = ;base.a[][] = ;

     base.a[][] = -;base.a[][] = ;

     ans = mul(ans,qpow(base,n-));

     ll res = (mod + ans.a[][]) % mod;

     cout<<res<<endl;

     return ;

 }