diff --git a/pyproject.toml b/pyproject.toml
index b3459f8..3e754f1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,7 +19,7 @@
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
   ]
-  dependencies = []
+  dependencies = ["numpy"]
   [project.optional-dependencies]
     dev = ["hatch", "mypy", "pre-commit", "pytest-cov", "pytest", "ruff", "tox"]
     docs = ["furo", "sphinx", "sphinx-copybutton"]
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..98f7200
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+numpy==2.1.1
diff --git a/src/python_package_template/main.py b/src/python_package_template/main.py
index 37084ee..f83de5c 100644
--- a/src/python_package_template/main.py
+++ b/src/python_package_template/main.py
@@ -4,6 +4,8 @@
 @author "Daniel Mizsak" <info@pythonvilag.hu>
 """
 
+import numpy as np
+
 
 def add_five(x: int) -> int:
     """Increment the input by 5.
@@ -26,4 +28,4 @@ def subtract_three(x: int) -> int:
     Returns:
         int: The input decremented by 3.
     """
-    return x - 3
+    return int(np.subtract(x, 3))