How to solve this problem regarding the const qualifier?

I have a function foo as follows

void Foo::foo(const Vertex & a, const Vertex & b, const Vertex & c) {

	Coordinate head;
	a.calcSomething(......);
}

an got the following error information when compiling:

Foo.cpp:156: error: passing 'const Vertex' as 'this' argument of
'const void Vertex::calcSomething(......)' discards qualifiers


How to solve this problem? Isn't it enough to put calcSomething in the
following way?

class Vertex{
const void calcSomething(...){
....
};
};