\begin{tikzpicture}[
    box/.style={draw, minimum width=1.5cm, minimum height=0.8cm},
    arrow/.style={->, >=latex},
    font=\small
]
    % CP regression part
    \node[box,fill=white] (cp) at (0,0) {\large CP for Regression};
    \node[box,fill=white] (k) at (0,-2) {\large $\hat{K}$};
    \node[left=0.3cm of k] {\large Calibrated stopping rule};
    \node[box,fill=white] (f) at (0,2) {\large $\hat{f}$};
    \node[left=0.3cm of f] {\large Admissibility predictor};
    
    % Add input box with connecting arrows
    \node[box,fill=white] (input) at (-4,0) {$\{(X_i, K_i)\}_{i=1}^n$};
    % \draw[arrow] (-6,0) -- (input);
    \draw[arrow] (input) -- (cp);
    
    % Connect f hat from top
    \draw[arrow] (f) -- (cp);
    
    % Connect CP to K
    \draw[arrow] (cp) -- (k);
\end{tikzpicture} 