# include <stdio.h>

int f[10];

int main()

{

	int x,y,n,j;

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

	{

		f[1]=x;

		f[2]=y;

        for(j=3;j<=6;j++)

		{

			f[j]=f[j-1]-f[j-2];

		}

		n%=6;

		if(n==0)

			n=6;

		if(f[n]>=0)

			    printf("%d\n",f[n]%1000000007);

		else

			while(f[n]<0)//注意负数取模  然后就没有然后了~~~~~

				f[n]+=1000000007;

		     	printf("%d\n",f[n]%1000000007);

	}

	return 0;

}