function X = first(A, B)
     r = rows(A)
     c = columns(A)
     Ag = [A B]

     if (rank(A) == rank(Ag))
          if (rank(A) == c)
               disp("Единственное решение")
               for k = 1:r
                    if (Ag(k,k) != 0)
                         Ag(k,:) = Ag(k,:) /Ag(k,k)
                         for i = k + 1:c
                              Ag(i,:) = Ag(i,:)  - Ag(k,:)*Ag(i,k);
                         endfor
                    else
                         disp("Деление на ноль")
                    endif
               endfor
               X = Ag(end,end)
               for k = r - 1:-1:1
                    X = [Ag(k, c + 1) - sum(Ag(k, c - (length(X) - 1) : c) * X); X]
               endfor
          else
               disp("Неопределена")
          endif
     else
          disp("Нет решений")
     endif

end