\documentclass[a4paper,11pt]{article}

\usepackage{ngerman}
\usepackage{amsmath,amsfonts,amssymb,amsthm}

\usepackage{tikz}
\usetikzlibrary{arrows,chains,matrix,positioning,scopes}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{math}

\def\O{\mathcal{O}}
\def\sort{\mathrm{sort}}
\def\scan{\mathrm{scan}}
\def\dist{\mathrm{dist}}
\def\Z{\mathbb{Z}}
\def\Q{\mathbb{Q}}
\def\R{\mathbb{R}}
\def\E{\mathbb{E}}


\begin{document}


\textbf{Aufgabe 4}
\begin{center}
	\begin{tikzpicture}
	\node[draw,circle] at (0, 0) (s) {$s$};
	\node[draw,circle] at (3, 0) (u) {$v$};
	\node[draw,circle] at (3, 3) (t) {$t$};
	\node[draw,circle] at (0, 3) (v) {$u$};
	
	\path[->,>=triangle 60,shorten >=0pt,every node/.style={font=\small}]
	(s) edge node[above,sloped, pos=0.3] () {0.6} (t)
	edge node[left] () {0.6} (v)
	(v) edge node[above] () {0.1} (t)
	edge node[above,sloped, pos=0.7] () {0.5} (u)
	(u) edge node[below] () {0.2} (s)
	edge node[right] () {0.3} (t)
	;
	\end{tikzpicture}  
\end{center}


\end{document}