x, y = map(int, input().split())
n = int(input())
lst = [x, y]
i = 1
while i < 6:
p = lst[i] - lst[i-1]
lst.append(p)
i += 1
ans = lst[(n-1)%6]
print(ans%(10**9 + 7))#include <bits/stdc++.h>
using namespace std;
const int num=1e9+7;
int main()
{
int x,y;
cin>>x>>y;
long long n;cin >>n;
if(x<0)
x+=num;
if(y<0)
y+=num;
int z=(y%num-x%num +num)%num;
int rem=n%6;
if(rem==0)
cout<<(-z+num)%num<<"\n";
if(rem==1)
cout<<x<<"\n";
if(rem==2)
cout<<y<<"\n";
if(rem==3)
cout<<z<<"\n";
if(rem==4)
cout<<(-x+num)%num<<"\n";
if(rem==5)
cout<<(-y+num)%num<<"\n";
}
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