c# fighting question

first, twin examples:

// works
int foo = 43;
long lfoo = foo;

// doesn't
object foo = (int)43;
long? nullfoo = foo long?; // advantage null
long lfoo = (long)foo; // throws invalidcastexception
if (foo.gettype() == typeof(int))
    console.writeline("but foo an int..."); // gets combined out

now, speculation since second doesn't work since boxing. purpose behind formula exercise icomparable. i need proceed need an vigilant presumably enlarged ulong appropriate, it's neither, pitch an error. i don't wish have exercise checks any simple numeric form (byte, int, long, ubyte, ...) i'd rather only locate largest numeric form understanding way. thoughts intelligent here? i unbox object, preferably avoiding reflection, nonetheless i suspect that's wholly way... should i only exercise non-generics chronicle icomparable?

edit:

this seems work, nonetheless seems terrible penetrate around problem. only me?

long lfoo = long.parse(foo.tostring());