input: Write a function to convert a given Python program to a C# program. The function should take a Python function as input and return a C# function equivalent to it. The function should handle the basic structure of the Python function, including the name, parameters, return type, and logic. 
  public string ConvertPythonToCSharp(string pythonCode)
  assert ConvertPythonToCSharp("def power(x, y):\n    if y == 0:\n        return 1\n    else:\n        return x * power(x, y - 1)")=="public int Power(int x, int y)\n{\n    if (y == 0)\n    {\n        return 1;\n    }\n    else\n    {\n        return x * Power(x, y - 1);\n    }\n}"
  assert ConvertPythonToCSharp("def add(a, b):\n    return a + b")=="public int Add(int a, int b)\n{\n    return a + b;\n}"
  assert ConvertPythonToCSharp("")=="The input Python function is empty."
  assert ConvertPythonToCSharp("def greet(name):\n    return 'Hello, ' + name")=="public string Greet(string name)\n{\n    return 'Hello, ' + name;\n}"
output: 
  def ConvertPythonToCSharp(pythonCode):
      if not pythonCode.strip():
          return "The input Python function is empty."
      
      lines = pythonCode.split('\n')
      if not lines[0].startswith("def "):
          return "The input is not a valid Python function."
      
      func_def = lines[0][4:].split('(')
      func_name = func_def[0]
      params = func_def[1].split(')')[0].split(',')
      param_types = ['int ' + p.strip() if p.strip().isalpha() else 'string ' + p.strip() for p in params]
      param_string = ', '.join(param_types)
      
      return_type = 'int' if 'return ' in pythonCode and 'return ' + func_name in pythonCode else 'string'
      
      csharp_code = f"public {return_type} {func_name.capitalize()}({param_string})\n{{\n"
      
      for line in lines[1:]:
          if line.strip().startswith('return '):
              return_statement = line.strip()[7:]
              if return_type == 'string':
                  return_statement = f"'{return_statement}'"
              csharp_code += f"    return {return_statement};\n"
          elif line.strip().startswith('if '):
              condition = line.strip()[3:].replace('==', '===').replace('!=', '!==')
              csharp_code += f"    if ({condition})\n    {{\n"
          elif line.strip().startswith('else:'):
              csharp_code += "    }\n    else\n    {\n"
          elif line.strip().startswith('return '):
              return_statement = line.strip()[7:]
              if return_type == 'string':
                  return_statement = f"'{return_statement}'"
              csharp_code += f"    return {return_statement};\n"
      
      csharp_code += "}"
      return csharp_code
  