#include <iostream.h>
#include <stdio.h>
int main()
{
unsigned   __int64   sum;
unsigned   __int64   res;
scanf("%I64d",&sum);
res = sum % 7;
printf("%I64d\n",res);
return 0;
}

Do you really think that unsigned __int64 consist of 10^50 digits?? :) You should use long arithmetics, or strings. Think about it.

Thank you!