class Graph:
    def __init__(self):
        self.nodes = {}
    
    def neighbors(self, id):
        return self.nodes[id][0]

    def direction2point(self, point, direction):
        if direction == 'N':
            return (point[0] - 1, point[1])
        elif direction == 'S':
            return (point[0] + 1, point[1])
        elif direction == 'W':
            return (point[0], point[1] - 1)
        else:
            return (point[0], point[1] + 1)

    def add_neighbor(self, node, direction):
        neighbor = self.direction2point(node, direction)
        if node in self.nodes:
            self.nodes[node][0].add(neighbor)
        else:
            self.nodes[node] = (set([neighbor]), False)
        if neighbor in self.nodes:
            self.nodes[neighbor][0].add(node)
        else:
            self.nodes[neighbor] = (set([node]), False)