Update cf-100886G.mdx

Author: xyzqm

solutions/gold/cf-100886G.mdx

@@ -35,7 +35,7 @@ using namespace std;
 
 /** @return the product of the given string's digits (-1 if empty) */
 ll prod(string s) {
-	if (!s.length()) return -1;
+	if (!s.length()) { return -1; }
 	ll res = 1;
 	for (char c : s) { res *= c - '0'; }
 	return res;