#include <iostream>
using namespace std;

struct foo {
	int& a;
	foo(int& b) : a(b) {}
	void bar() const {
		a = 5;
	}
};


int main() {
	int x = 10;
	cout << x << endl;
	const foo f(x);
	f.bar();
	cout << x << endl;
	return 0;
}