import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.io.PrintStream;
import java.util.Map;
import java.util.Scanner;


public class Check10D
{
	public static void main(String[] args) throws Exception
	{
		PrintStream output = System.out;
		Scanner input = new Scanner(System.in);
		
		output.print("Filename of the graph... ");
		String filename = input.nextLine();
		
		// the graph
		Map<String, Double> graph = null;

		FileInputStream fis = new FileInputStream(filename);
		ObjectInputStream ois = new ObjectInputStream(fis);
		Object obj = ois.readObject();
		if (obj instanceof Map)
		{
			graph = (Map<String, Double>) obj;
		}
		output.println(graph.size());
	}
}