codeforces 257B

#include<stdio.h>
#define mod 1000000007
int main() {
 __int64 n,m,i,j,k,x,y,z;
 while(scanf("%I64d%I64d%I64d",&x,&y,&n)!=EOF) {
    z=y-x;
    i=n%3;
    j=n/3;
    if(i==0) {
        i=3;
        j--;
    }
    if(i==3)  {
            if(j%2==1)
            z=-z;
while(z<0)//用循环写
z+=mod;
            printf("%I64d\n",z%mod);
    }
    else
         if(i==2)  {
                if(j%2==1)
                y=-y;
while(y<0)//用循环写
y+=mod;
            printf("%I64d\n",y%mod);
         }
          if(i==1) {
                if(j%2==1)
                x=-x;
while(x<0)//用循环写
x+=mod;
      printf("%I64d\n",x%mod);
          }

 }
return 0;
}