using System;

public interface Foo
{
    Foo foo();
}

class Foo_int : Foo
{
    private int content = 0;
    
    public Foo_int(int content)
    {
        this.content = content;
    }
    
    public Foo foo()
    {
        return new Foo_int(content + 1);
    }
    
    public override string ToString()
    {
        return content.ToString();
    }
}

public class Test
{
    public static Foo bar(Foo x)
    {
        return x.foo();
    }
    
    public static void Main()
    {
        var x = new Foo_int(1);
        Console.WriteLine(bar(x));
    }
}