#include <cstddef>

namespace Sample {

template <typename T, const size_t N, const size_t M>
class Matrix {
private:
    class Row {
    private:
        T row[M];

    public:
        const T & operator[] (size_t i) const {
            return row[i];
        }

        T & operator[] (size_t i) {
            return row[i];
        }
    };

    Row data[N];

public:
    const Row & operator[] (size_t i) const {
        return data[i];
    }

    Row & operator[] (size_t i) {
        return data[i];
    }

};

}