#include <iostream>
#include <cstdio>
using namespace std;

int main() {
	long long int x, y, z, n, tmp, a[7]={0}, ans;
	const int md=1e9+7;
	scanf("%lld%lld", &x, &y);
	scanf("%lld", &n);
	z=y-x, a[1]=x, a[2]=y;
	for(int i=3; i<=6; i++) {
		tmp=x, x=y, y=z, z=y-x, a[i%6]=y;
	}
	if(a[n%6]>=0) printf("%lld", a[n%6]%md);
	else printf("%lld", (md+a[n%6]%md)%md);
	return 0;
}