diff --git a/task_01/src/main.cpp b/task_01/src/main.cpp
index 0e4393ba..3919ad50 100644
--- a/task_01/src/main.cpp
+++ b/task_01/src/main.cpp
@@ -1,3 +1,8 @@
 #include <iostream>
 
-int main() { return 0; }
+#include "utils.hpp"
+
+int main() {
+  std::cout << "Hello World\n";
+  return 0;
+}
diff --git a/task_01/src/test.cpp b/task_01/src/test.cpp
index ef5a86ae..6b6b60d4 100644
--- a/task_01/src/test.cpp
+++ b/task_01/src/test.cpp
@@ -1,8 +1,21 @@
-
 #include <gtest/gtest.h>
 
-#include "topology_sort.hpp"
+#include "utils.hpp"
 
-TEST(TopologySort, Simple) {
-  ASSERT_EQ(1, 1);  // Stack []
+TEST(utils, Simple) {
+  ASSERT_EQ(FindSum(10, std::vector<int>{2, 3, 4, 7, 12}),
+            (std::pair<int, int>{3, 7}));
+  ASSERT_EQ(
+      FindSum(27, std::vector<int>{1, 2, 4, 5, 8, 10, 13, 17, 20, 21, 22, 25}),
+      (std::pair<int, int>{2, 25}));
+  ASSERT_EQ(FindSum(6, std::vector<int>{1, 5, 13, 21, 22}),
+            (std::pair<int, int>{1, 5}));
+  EXPECT_THROW(FindSum(7, std::vector<int>{1, 5, 13, 21, 22}),
+               std::logic_error);
+  EXPECT_THROW(FindSum(57, std::vector<int>{2, 3, 4, 7, 12}), std::logic_error);
+  EXPECT_THROW(
+      FindSum(-3, std::vector<int>{1, 2, 4, 5, 8, 10, 13, 17, 20, 21, 22, 25}),
+      std::logic_error);
+  EXPECT_THROW(FindSum(120, std::vector<int>{}), SmallVector);
+  EXPECT_THROW(FindSum(47, std::vector<int>{1}), SmallVector);
 }
diff --git a/task_01/src/topology_sort.cpp b/task_01/src/topology_sort.cpp
deleted file mode 100644
index e53f670c..00000000
--- a/task_01/src/topology_sort.cpp
+++ /dev/null
@@ -1 +0,0 @@
-#include "topology_sort.hpp"
diff --git a/task_01/src/topology_sort.hpp b/task_01/src/topology_sort.hpp
deleted file mode 100644
index 6f70f09b..00000000
--- a/task_01/src/topology_sort.hpp
+++ /dev/null
@@ -1 +0,0 @@
-#pragma once
diff --git a/task_01/src/utils.cpp b/task_01/src/utils.cpp
new file mode 100644
index 00000000..fd5d7d2f
--- /dev/null
+++ b/task_01/src/utils.cpp
@@ -0,0 +1,25 @@
+#include "utils.hpp"
+
+#include <iostream>
+#include <stdexcept>
+#include <vector>
+
+std::pair<int, int> FindSum(int number, const std::vector<int> array) {
+  if (array.size() < 2) {
+    throw SmallVector("vector size is too small");
+  }
+  int left_index = 0;
+  int right_index = array.size() - 1;
+  while (left_index < right_index) {
+    int sum = array[left_index] + array[right_index];
+    if (sum == number) {
+      return std::make_pair(array[left_index], array[right_index]);
+    }
+    if (sum < number) {
+      left_index++;
+    } else {
+      right_index--;
+    }
+  }
+  throw std::logic_error("no indexes found");
+}
\ No newline at end of file
diff --git a/task_01/src/utils.hpp b/task_01/src/utils.hpp
new file mode 100644
index 00000000..ebec21d9
--- /dev/null
+++ b/task_01/src/utils.hpp
@@ -0,0 +1,9 @@
+#pragma once
+#include <iostream>
+#include <vector>
+
+class SmallVector : public std::runtime_error {
+  using std::runtime_error::runtime_error;
+};
+
+std::pair<int, int> FindSum(int number, std::vector<int> array);
\ No newline at end of file