HDU 1005 Number Sequence

#include <cstdio>
int main(){
int a,b,n,f[50]; f[1]=f[2]=1;
while(scanf("%d%d%d",&a,&b,&n),a|b|n){
int t1,t2,bo=0;
for(int i=3;i<=n&&!bo;i++){
f[i]=(a*f[i-1]+b*f[i-2])%7;
for(int j=2;j<=i-1;j++)if(f[i]==f[j]&&f[i-1]==f[j-1]){t1=j,t2=i;bo=1;break;}
}if(bo)printf("%d\n",f[t1+(n-t2)%(t2-t1)]);else printf("%d\n",f
);
}
return 0;
}