import collections

n = 3
edges = [[0,1,100],[1,2,200],[0,2,500]]
src = 0
dst = 2
k = 1



def findCheapestPrice(n, flights, src, dst, K):

    if src == dst: return 0

    d, seen = collections.defaultdict(list), collections.defaultdict(lambda: float('inf'))
    for u, v, p in flights:
        d[u] += [(v, p)]

    q = [(src, -1, 0)]
    
    while q:
        pos, k, cost = q.pop(0)
        if pos == dst or k == K: continue 
        for nei, p in d[pos]:
            if cost + p >= seen[nei]:
                continue
            else:
                seen[nei] = cost+p
                q += [(nei, k+1, cost+p)]
            
    return seen[dst] if seen[dst] < float('inf') else -1

print( findCheapestPrice(n, edges, src, dst, k) )