Реализую алгоритм Дейкстры для такого графа. Ответ должен быть 8, у меня 9. Не пойму в чём ошибка

graph = {}
graph['s'] = {}
graph['s']['A'] = 5; graph['s']['B'] = 2 

graph['A'] = {} 
graph['A']['C'] = 4; graph['A']['D'] = 2

graph['B'] = {} 
graph['B']['A'] = 8; graph['B']['D'] = 7 

graph['C'] = {} 
graph['C']['f'] = 3; graph['C']['D'] = 6 

graph['D'] = {} 
graph['D']['f'] = 1 

graph['f'] = {}

costs = {} 
costs['A'] = 5; costs['B'] = 2 
costs['C'] = costs['D'] = costs['f'] = float('inf') 

parents = {} 
parents['A'] = parents['B'] = 's'
parents['C'] = parents['D'] = parents['f'] = None

processed = [] 

def find_lowest_cost_node(costs):
    lowest_cost = float('inf')
    lowest_cost_node = None 
    for node in costs:
        cost = costs[node] 
        if cost < lowest_cost and node not in processed:
             lowest_cost = cost
             lowest_cost_node = node 
    return lowest_cost_node

node = find_lowest_cost_node(costs)
while node is not None:
    cost = costs[node] 
    neighbors = graph[node] 
    for n in neighbors.keys():
        new_cost = cost + neighbors[n] 
        if costs[n] > new_cost: 
            costs[n] = new_cost 
            parents[n] = node 
    processed.append(node)
    node = find_lowest_cost_node(costs) 
print(cost)