def dijkstra(G):
    now = 0
    stack.append(G)
    for i in my_list[G]:
        if i[1] >= now:
            stack.append(i)
    while stack != list():
        end = stack.pop()
        used = [False] * N
        for i in end:
            dad
            if i[0] != dad:
                time += i[2]
                stack.append(i)
                used[i] = True
        dad = end[0]


N = int(input())
d, v = map(int, input().split())
R = int(input())
my_list = [list() for _ in range(N)]
for i in range(R):
    line = list(map(int, input().split()))
    my_list[line[0] - 1].append([line[2] - 1, line[1], line[3]])
stack = list()
dijkstra(d)