diff --git a/modules/13_cpp23/src/expected.cpp b/modules/13_cpp23/src/expected.cpp
index 5e54f85..2be011e 100644
--- a/modules/13_cpp23/src/expected.cpp
+++ b/modules/13_cpp23/src/expected.cpp
@@ -1,20 +1,34 @@
 #include "expected.hpp"
 
+#include <cmath>
+
 namespace cpp23 {
 
 auto parse_int(const std::string& text) -> std::expected<int, ParseError> {
-    (void)text;
-    return std::unexpected(ParseError::EmptyInput);
+    if (text.empty()) {
+        return std::unexpected(ParseError::EmptyInput);
+    }
+    try {
+        const auto i = std::stoi(text);
+        return i;
+    }
+    catch (const std::invalid_argument&) {
+        return std::unexpected(ParseError::InvalidNumber);
+    }
+    catch (const std::out_of_range&) {
+        return std::unexpected(ParseError::InvalidNumber);
+    }
 }
 
-auto safe_sqrt(int value) -> std::expected<double, std::string> {
-    (void)value;
-    return std::unexpected(std::string{"negative"});
+auto safe_sqrt(const int value) -> std::expected<double, std::string> {
+    if (value < 0) {
+        return std::unexpected(std::string{"negative"});
+    }
+    return std::sqrt(value);
 }
 
 auto chain_parse_and_double(const std::string& text) -> std::expected<int, ParseError> {
-    (void)text;
-    return std::unexpected(ParseError::InvalidNumber);
+    return parse_int(text).transform([](const auto i) { return i * 2; });
 }
 
 }  // namespace cpp23