import std.stdio;

class Graph
{
    size_t capacity;
    size_t nodesCount;
    Node nodes;

    Node add_node()
    {
        auto node = new Node(nodesCount);
        if (nodes is null)
        {
            nodes = node;
        }
        else
        {
            auto crnt = nodes;
            while (crnt.next !is null)
            {
                crnt = nodes.next;
            }
            crnt.next = node;
        }
        nodesCount++;
        return node;
    }

    void add_edge(size_t from, size_t to, size_t shift, double weight)
    {
        Node nodeFrom;
        Node nodeTo;
        auto crnt = nodes;
        size_t done = 0;
        while (crnt !is null)
        {
            if (done == from)
            {
                nodeFrom = crnt;
            }
            if (done == to)
            {
                nodeTo = crnt;
            }
            crnt = crnt.next;
            done++;
        }
        auto edge = new Edge(shift, weight, nodeTo);
        if (nodeFrom.edges is null)
        {
            nodeFrom.edges = edge;
        }
        else
        {
            auto crntEdge = nodeFrom.edges;
            while (crntEdge.next !is null)
            {
                crntEdge = crntEdge.next;
            }
            crntEdge.next = edge;
        }
    }

    void eval(size_t i)
    {
        auto node = nodes;
        while (node !is null)
        {
            auto val = (i % 2 == 0) ? node.value0 : node.value1;
            auto edge = node.edges;
            while (edge !is null)
            {
                if (i % 2 == 0 && edge.shift == 0)
                {
                    edge.to.value0 += val * edge.weight;
                }
                else if (i % 2 == 0 && edge.shift == 1)
                {
                    edge.to.value1 += val * edge.weight;
                }
                else if (i % 2 == 1 && edge.shift == 0)
                {
                    edge.to.value1 += val * edge.weight;
                }
                else if (i % 2 == 1 && edge.shift == 1)
                {
                    edge.to.value0 += val * edge.weight;
                }
                edge = edge.next;
            }
            node.res = val;
            if (i % 2 == 0)
            {
                node.value0 = 0;
            }
            else
            {
                node.value1 = 0;
            }
            node = node.next;
        }
    }
}

class Node
{
    size_t id;
    Node next;
    double value0;
    double value1;
    double res;
    Edge edges;

    this(size_t id)
    {
        this.id = id;
        this.res = 0;
        this.value0 = 0;
        this.value1 = 0;
    }
}

class Edge
{
    Edge next;
    Node to;
    size_t shift;
    double weight;

    this(size_t shift, double weight, Node to)
    {
        this.shift = shift;
        this.weight = weight;
        this.to = to;
    }
}

void main()
{
    auto g = new Graph();
    auto n1 = g.add_node();
    auto n2 = g.add_node();

    g.add_edge(0, 1, 0, 0.5);
    g.add_edge(1, 1, 1, 0.5);

    foreach(i; 0..3) {
        n1.value0 = 1.0;
    	n1.value1 = 1.0;
		g.eval(i%2);
    }
    writeln(n2.res);
}