template <int size>
struct FileBuffer {
    char buffer[size];
    FILE *file;

    int offset;

    FileBuffer (const char *fileName) {
        file = fopen(fileName, "r");
        offset = -1;
    }

    ~FileBuffer() {
        fclose(file);
    }

    void load(int offset) {
        fseek(file, offset, 0);
        fread(buffer, 1, size, file);
        this->offset = offset;
    }

    char &operator[](int pos) {
        if (offset == -1 || !(pos > offset && pos - offset < size)) {
            load(pos);
        }
        return buffer[pos - offset];
    }

};