\documentclass[a4]{article}
\usepackage{tikz}
\begin{document}
\begin{center}
\begin{tikzpicture}[ scale=2,radius=1pt]
\draw [<-,thick] (0,2) -- (0,0);
\draw [->,thick] (0,0) -- (4,0);
\draw[dashed](1,0)--(1,2);

    \draw (0 cm,1pt) -- (0 cm,-1pt) node[anchor=north] {$0$};
    \draw (1 cm,1pt) -- (1 cm,-1pt) node[anchor=north] {$b$};
    \draw (2 cm,1pt) -- (2 cm,-1pt) node[anchor=north] {$c$};
    \draw (3 cm,1pt) -- (3 cm,-1pt) node[anchor=north] {$d$};
    
    \draw [-,thick] (1.05,1.8)  to [out=-80,in=-200] (2,1) circle ;
    \draw [-,thick]  (2,1.5)  to [out=20,in=-100] (2.5,2) node[xshift=-1.05cm,yshift=-1.05cm]{$\circ$};
        \draw [-,thick]  (2.5,2)  to [out=-80,in=-180] (3,1.5) ;
\end{tikzpicture}
\end{center}
\end{document}