%\documentclass{standalone}
\documentclass[convert={density=800,size=600x300,outext=.png}]{standalone}
\usepackage{amsmath}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\usetikzlibrary{calc}
\usetikzlibrary{positioning}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{math} % tikzmath, see p. 640 of the pgfmanual.
\usetikzlibrary{arrows}
\usepackage{svgcolor} 
\begin{document}
\begin{tikzpicture}
%\useasboundingbox (-2,-2.8) rectangle (10,2.8);
\filldraw[white] (-0.5,-0.5) rectangle (5.9,3.5);
\tikzstyle{vrh}=[draw,circle,fill=yellow,text=black]
\node[vrh] (a) at (0,0) {$a$};
\node[vrh] (c) at (3.2,0) {$c$};
\node[vrh] (e) at (5.5,1.5) {$e$};
%\node[vrh] (v6) at (-1.5,1.5) {$v_6$};
\node[vrh] (b) at (0,3) {$b$};
\node[vrh] (d) at (3.2,3) {$d$};
\draw[->,>=stealth'] (a)--(c) node[pos=0.5,fill=white,inner sep=2pt] {$-1$};
%\draw[->,>=stealth'] (v6)--(a) node[pos=0.5,fill=white,inner sep=2pt] {$15$};
\draw[->,>=stealth'] (a) to[bend left=15] node[pos=0.5,fill=white,inner sep=4pt] {$3$} (b);
\draw[->,>=stealth'] (b) to[bend left=15] node[pos=0.5,fill=white,inner sep=4pt] {$2$} (a);
\draw[->,>=stealth'] (b) to[bend left=18] node[pos=0.5,fill=white,inner sep=4pt] {$2$} (d);
\draw[->,>=stealth'] (d) to[bend left=18] node[pos=0.5,fill=white,inner sep=4pt] {$-2$} (b);
\draw[->,>=stealth'] (c) to[bend left=15] node[pos=0.5,fill=white,inner sep=4pt] {$4$} (d);
\draw[->,>=stealth'] (d) to[bend left=15] node[pos=0.5,fill=white,inner sep=4pt] {$2$} (c);
\draw[->,>=stealth'] (c)--(b) node[pos=0.5,fill=white,inner sep=2.5pt] {$1$};
\draw[->,>=stealth'] (d)--(e) node[pos=0.5,fill=white,inner sep=2.5pt] {$-3$};
\draw[->,>=stealth'] (c) -- (e) node[pos=0.5,fill=white,inner sep=2pt] {$6$};
\end{tikzpicture}
\end{document}