Can't draw arrows with tikz

Question

I am drawing a block diagram for a controllable canonical form, and for some reason I am not able to draw arrows between blocks.

\documentclass[a4paper]{article}
\usepackage[spanish]{babel}
\usepackage{float}
\usepackage{tikz}
\usetikzlibrary{shapes, arrows}
\tikzset{
    block/.style    = {draw, thick, rectangle, minimum height = 3.5em, minimum width = 3.5em},
    sum/.style      = {draw, circle, node distance = 2cm, minimum size = 3.5em}, % Adder
    gain1/.style     = {draw, isosceles triangle, isosceles triangle apex angle=45, minimum height = 3em, shape border rotate=180, inner sep=1},
    gain/.style     = {draw, isosceles triangle, isosceles triangle apex angle=45, minimum size = 3em, inner sep=1},
    input/.style    = {coordinate}, % Input
    output/.style   = {coordinate} % Output
}
\begin{document}
\begin{figure}[H]
    \centering
    \begin{tikzpicture}[auto, thick, node distance=2cm]
        \draw
        node [input, name=input1] {}
        node [sum, right of=input1] (integrador1) {\Large $\sum$}
        node [block, right of=integrador1] (x1) {$1/s$}
        node [gain1, below of=x1] (a3) {$-10$}
        node [block, right of=x1] (x2) {$1/s$}
        node [gain1, below of=x2, below=5mm] (a2) {$-35$}
        node [gain, above of=x2, above=13mm] (b3) {$0$}
        node [block, right of=x2] (x3) {$1/s$}
        node [gain1, below of=x3, below=13mm] (a1) {$-50$}
        node [gain, above of=x3, above=5mm] (b2) {$0$}
        node [sum, right of=b2, right=40mm] (integrador2) {\Large $\sum$}
        node [block, right of=x3] (x4) {$1/s$}
        node [gain1, below of=x4, below=21mm] (a0) {$-24$}
        node [gain, above of=x4] (b1) {$1$}
        node [gain, right of=b1, below=5mm] (b0) {$-1$};
    \draw[->] (x1) -- (x2);
\end{tikzpicture}
\caption{Representación de la forma canónica controlable}

\end{figure}
\end{document}

I get 7 errors on the \draw[->] (x1) -- (x2); line, which is just an arrow I am trying to draw between the blocks x1 and x2.

The errors I get are listed below:

• Argument of \language@active@arg> has an extra }. <inserted text>
• Paragraph ended before \language@active@arg> was complete. <to be read again>
• Paragraph ended before \pgfkeys@addpath was complete. <to be read again>
• Missing \endcsname inserted. <to be read again>
• Missing \endcsname inserted. <to be read again>
• Missing \endcsname inserted. <to be read again>
• Paragraph ended before \pgfkeys@splitter was complete. <to be read again>

Is there a reason why I am getting these errors? How can I fix it?

Thanks in advance.