In C++ if I wanted to denote a 64-bit numeral I'd add LL at the end as such:
__int64 n = 1000000LL * 10000LL;
Is there a way to do the same in C#?
Very similar
Int64 n = 1000000L * 10000L;
Which is really a long
long n = 1000000L * 10000L;
    public static void Main(string[] args)
    {
        //Your code goes here
        Int64 num = 1000000L * 10000L;
        long n = 1000000L * 10000L;
        Console.WriteLine(num*n);
    }
Will print 7766279631452241920