diff --git a/SharpCalculator.sln b/SharpCalculator.sln
index b20003b..353d5f3 100644
--- a/SharpCalculator.sln
+++ b/SharpCalculator.sln
@@ -2,6 +2,8 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SharpCalculator.Avalonia", "SharpCalculator.Avalonia\SharpCalculator.Avalonia.csproj", "{93E7D002-22D7-4C4F-AE6B-F1E0D938BCBA}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SharpCalculator", "SharpCalculator\SharpCalculator.csproj", "{F41EEE99-5319-4AAF-BB10-C82FE4E0557B}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -12,5 +14,9 @@ Global
 		{93E7D002-22D7-4C4F-AE6B-F1E0D938BCBA}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{93E7D002-22D7-4C4F-AE6B-F1E0D938BCBA}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{93E7D002-22D7-4C4F-AE6B-F1E0D938BCBA}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F41EEE99-5319-4AAF-BB10-C82FE4E0557B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F41EEE99-5319-4AAF-BB10-C82FE4E0557B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F41EEE99-5319-4AAF-BB10-C82FE4E0557B}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F41EEE99-5319-4AAF-BB10-C82FE4E0557B}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal
diff --git a/SharpCalculator/IExpression.cs b/SharpCalculator/IExpression.cs
new file mode 100644
index 0000000..44bf625
--- /dev/null
+++ b/SharpCalculator/IExpression.cs
@@ -0,0 +1,6 @@
+namespace SharpCalculator;
+
+public interface IExpression
+{
+    public double Calculate();
+}
\ No newline at end of file
diff --git a/SharpCalculator/NumericExpression.cs b/SharpCalculator/NumericExpression.cs
new file mode 100644
index 0000000..204300a
--- /dev/null
+++ b/SharpCalculator/NumericExpression.cs
@@ -0,0 +1,13 @@
+namespace SharpCalculator;
+
+public class NumericExpression : IExpression
+{
+    private double n;
+
+    public NumericExpression(double n)
+    {
+        this.n = n;
+    }
+
+    public double Calculate() => n;
+}
\ No newline at end of file
diff --git a/SharpCalculator/SharpCalculator.csproj b/SharpCalculator/SharpCalculator.csproj
new file mode 100644
index 0000000..e1fafe4
--- /dev/null
+++ b/SharpCalculator/SharpCalculator.csproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>netstandard2.0</TargetFramework>
+        <LangVersion>12</LangVersion>
+        <ImplicitUsings>disable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+</Project>