#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=100000+10;
const ll MOD =1000000007 ;
struct Mar
{
ll mat[2][2];
Mar operator *(const Mar &m )const
{
Mar tmp;
for(int i=0;i<2;i++)
{
for(int j=0;j<2;j++)
{
tmp.mat[i][j]=0;
for(int k=0;k<2;k++)
{
tmp.mat[i][j]=(tmp.mat[i][j]%MOD+mat[i][k]*m.mat[k][j]%MOD)%MOD;
tmp.mat[i][j]%=MOD;
}
}
}
return tmp;
}
};
Mar quick(Mar a,ll b)
{
Mar ans;
memset(ans.mat,0,sizeof(ans.mat));
for(int i=0;i<2;i++)ans.mat[i][i]=1;
while(b)
{
if(b&1)
ans=ans*a;
b>>=1;
a=a*a;
}
return ans;
}
int main()
{
ll x,y,n;
scanf("%lld%lld%lld",&x,&y,&n);
Mar a;
memset(a.mat,0,sizeof(a.mat));
if(n==1)
{
printf("%lld\n",(x+MOD)%MOD);
return 0;
}
a.mat[0][0]=1;
a.mat[1][0]=1;
a.mat[0][1]=-1;
a.mat[1][1]=0;
Mar ans=quick(a,n-2);
// printf("%lld %lld\n",ans.mat[1][0],ans.mat[1][1]);
printf("%lld\n",((y%MOD*ans.mat[0][0]%MOD+MOD)%MOD+(x%MOD*ans.mat[0][1]%MOD+MOD)%MOD+MOD)%MOD);
return 0;
}
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