add solutions to problems #1 and #2

Program.cs

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+using System;
+using System.Collections.Generic;
+
+namespace Euler {
+
+  class Program {
+
+  	static int Problem1() {
+  		int sum = 0;
+  		for (int i = 1; i < 1000; i++) {
+  			if (i % 3 == 0 || i % 5 == 0) {
+  				sum += i;
+  			}
+  		}
+  		return sum;
+  	}
+
+  	static long Problem2() {
+  		int max = 4_000_000;
+
+  		var fibs = new List<int>();
+  		fibs.Add(1);
+  		fibs.Add(2);
+
+  		while (fibs[fibs.Count - 1] < max) {
+  			int num = fibs[fibs.Count - 1] + fibs[fibs.Count - 2];
+ 			  fibs.Add(num);
+  		}
+
+      int sum = 0;
+  		foreach (int i in fibs) {
+  			if (i % 2 == 0 && i <= max) {
+  				sum += i;
+  			}
+  		}
+
+  		return sum;
+  	}
+
+    static void Main(string[] args) {
+      Console.WriteLine(Problem2());
+    }
+  }
+}

euler.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>