def bfs(node, squares):
    visited = set()
    q = []
    q.append(node)
    sentinel = None
    q.append(sentinel)
    movement = 0
    while(len(q)>0):
        n = q.pop(0)
       
        if(n is sentinel):
            if(q):
                movement += 1
                q.append(sentinel)
                continue
            else:
                return -1
        if (n.finish):
            return movement
        if(n in visited):
            continue
        visited.add(n)
        for i in n.edges:
            q.append(squares[i])
            
def quickestWayUp(ladders, snakes):
    squares = {}
    dladders = {}
    dsnakes = {}
    for i in ladders:
        s1 = i[0]
        s2 = i[1]
        dladders[s1] = s2
    for i in snakes:
        s1 = i[0]
        s2 = i[1]
        dsnakes[s1] = s2
    for i in range(100, 0, -1):
        n = Node(i)
        squares[i] = n
        for j in range(i+1, i+7):
            if (j<=100):
                if(j in dladders):
                    n.edges.append(dladders[j])
                elif (j in dsnakes):
                    n.edges.append(dsnakes[j])
                else:
                    n.edges.append(j)  
    # for i in range(1,101):
    #     print("n", squares[i].val)
    #     print(squares[i].edges)
    squares[100].finish=True
    return bfs(squares[1], squares)