The sum of $n > 2$ nonzero real numbers (not necessarily distinct) equals zero. For each of the $2^n - 1$ ways to choose one or more of these numbers, their sums are written in non-increasing order in a row. The first number in the row is $S$. Find the smallest possible value of the second number.
1. Let \( x_1 \ge x_2 \ge \cdots \ge x_m > 0 > x_{m+1} \ge x_{m+2} \ge \cdots \ge x_n \) be the \( n \) numbers. Since all numbers are nonzero, \( n > 2 \) and \( \sum_{i=1}^n x_i = 0 \), we have \( n > m \ge 1 \).

2. Let \( S \) and \( T \) be the two first numbers in the row. We have:
   \[
   S = \sum_{i=1}^m x_i
   \]
   and
   \[
   T = S - \min(|x_m|, |x_{m+1}|)
   \]

3. Since \( S = \sum_{i=1}^m x_i \ge m x_m \), we have:
   \[
   |x_m| \le \frac{S}{m}
   \]

4. Given \( 0 = \sum_{i=1}^n x_i \le \sum_{i=1}^m x_i + (n-m)x_{m+1} \), we get:
   \[
   |x_{m+1}| \le \frac{S}{n-m}
   \]

5. Therefore:
   \[
   \min(|x_m|, |x_{m+1}|) \le \min\left(\frac{S}{m}, \frac{S}{n-m}\right) = \frac{S}{\max(m, n-m)}
   \]

6. Thus:
   \[
   T \ge S - \frac{S}{\max(m, n-m)}
   \]

7. For the smallest \( T \), we are looking for the smallest \( \max(m, n-m) \), which is \( \left\lceil \frac{n}{2} \right\rceil \).

8. This smallest value can indeed be reached, for example, with numbers:
   \[
   \overbrace{\frac{S}{\left\lceil \frac{n}{2} \right\rceil}, \cdots, \frac{S}{\left\lceil \frac{n}{2} \right\rceil}}^{\times \left\lceil \frac{n}{2} \right\rceil}, \overbrace{-\frac{S}{\left\lfloor \frac{n}{2} \right\rfloor}, \cdots, -\frac{S}{\left\lfloor \frac{n}{2} \right\rfloor}}^{\times \left\lfloor \frac{n}{2} \right\rfloor}
   \]

Hence, the answer is:
\[
\boxed{S - \frac{S}{\left\lceil \frac{n}{2} \right\rceil}}
\]