C#在X个字母数字值上拆分字符串

string input = "HelloWorld123";
int splitIndex = 5; // 假设X为5

string firstPart = input.Substring(0, splitIndex);
string secondPart = input.Substring(splitIndex);

Console.WriteLine("First part: " + firstPart); // 输出：Hello
Console.WriteLine("Second part: " + secondPart); // 输出：World123