For positive real numbers $a,$ $b,$ $c,$ and $d,$ find the minimum value of
\[\left\lfloor \frac{b + c + d}{a} \right\rfloor + \left\lfloor \frac{a + c + d}{b} \right\rfloor + \left\lfloor \frac{a + b + d}{c} \right\rfloor + \left\lfloor \frac{a + b + c}{d} \right\rfloor.\]
Let $S$ denote the given sum.  First, we apply the fact that for all real numbers $x,$ $\lfloor x \rfloor > x - 1.$

To see this, recall that any real number can be split up into its integer and fractional parts:
\[x = \lfloor x \rfloor + \{x\}.\]The fractional part of a real number is always less than 1, so $x < \lfloor x \rfloor + 1.$  Hence, $\lfloor x \rfloor > x - 1.$

Then
\begin{align*}
\left\lfloor \frac{b + c + d}{a} \right\rfloor &> \frac{b + c + d}{a} - 1, \\
\left\lfloor \frac{a + c + d}{b} \right\rfloor &> \frac{a + c + d}{b} - 1, \\
\left\lfloor \frac{a + b + d}{c} \right\rfloor &> \frac{a + b + d}{c} - 1, \\
\left\lfloor \frac{a + b + c}{d} \right\rfloor &> \frac{a + b + c}{d} - 1.
\end{align*}Adding these inequalities, we get
\begin{align*}
S &> \frac{b + c + d}{a} - 1 + \frac{a + c + d}{b} - 1 + \frac{a + b + d}{c} - 1 + \frac{a + b + c}{d} - 1 \\
&= \frac{a}{b} + \frac{b}{a} + \frac{a}{c} + \frac{c}{a} + \frac{a}{d} + \frac{d}{a} + \frac{b}{c} + \frac{c}{b} + \frac{b}{d} + \frac{d}{b} + \frac{c}{d} + \frac{d}{c} - 4.
\end{align*}By AM-GM, $\frac{a}{b} + \frac{b}{a} \ge 2.$  The same applies to the other pairs of fractions, so $S > 6 \cdot 2 - 4 = 8.$  As a sum of floors, $S$ itself must be an integer, so $S$ must be at least 9.

When $a = 4$ and $b = c = d = 5,$ $S = 9.$  Therefore, the minimum value of $S$ is $\boxed{9}.$