Ошибка в коде, как исправить?

#include <iostream>
#include <vector>
#include <algorithm>
 
static const double eps = 1e-15;
 
class rectangle
{
    double a{}, b{};
public:
    rectangle() = default;
    rectangle(double side_one, double side_two) :a(side_one), b(side_two) {};
 
    double side_one() ;const noexcept { return a; }
    double side_two() ;const noexcept { return b; }
    double& side_one() ;noexcept { return a; }
    double& side_two() n;oexcept { return b; }
 
    double diag() const noexcept { return std::sqrt(a * a + b * b); }
    double perimetr() const noexcept { return 2 * (a + b); }
    double square() const noexcept { return a * b; }
 
    bool is_square() const noexcept { return std::abs(a - b) < eps; }
};
 
int main()
{
    std::cout << "N = ";
    std::size_t N{};
    std::cin >> N;
 
    std::vector<rectangle> vr;
    double avg_square{};
    for (size_t i{}; i < N && std::cin; ++i)
    {
        rectangle rect;
        std::cout << "rect[" << i << "] a, b: ";
        std::cin >> rect.side_one() >> rect.side_two();
        avg_square += rect.square();
        vr.emplace_back(rect);
    }
    avg_square /= vr.size();
 
    std::cout << "count of rects with square more then average " << std::count_if(vr.begin(), vr.end(), [avg_square](const rectangle& rect)
    {
        return rect.square() > avg_square;
    }) << std::endl;
}

    double side_one() ;const noexcept { return a; }

    double side_one() const noexcept { return a; }
    double side_two() const noexcept { return b; }
    double& side_one() noexcept { return a; }
    double& side_two() noexcept{ return b; }

#include <iostream>
#include <vector>
#include <algorithm>
 
static const double eps = 1e-15;
 
class rectangle
{
    double a, b;
public:
    rectangle() :a(0), b(0) {}
    rectangle(double side_one, double side_two) :a(side_one), b(side_two) {};
 
    double side_one() { return a; }
    double side_two(){ return b; }
 
    double diag()  { return std::sqrt(a * a + b * b); }
    double perimetr()  { return 2 * (a + b); }
    double square() { return a * b; }
 
    bool is_square() { return std::abs(a - b) < eps; }
};
 
double avg_square = 0;
bool ff(rectangle rect)
{
    return rect.square() > avg_square;
}
int main()
{
    std::cout << "N = ";
    std::size_t N;
    std::cin >> N;
 
    std::vector<rectangle> vr;
    for (size_t i=0; i < N ; ++i)
    {
        std::cout << "rect[" << i << "] a, b: ";
        double a, b;
        std::cin >> a >> b;
        if (!std::cin)
            break;
        rectangle rect(a,b);
        avg_square += rect.square();
        vr.push_back(rect);
    }
    avg_square /= vr.size();
    N = std::count_if(vr.begin(), vr.end(), ff);
 
    std::cout << "count of rects with square more then average " << N << std::endl;
    return 0;
}