def main(): N, M = map(int, input().split()) from collections import defaultdict edges = defaultdict(list) for _i in range(M): frm, to = map(int, input().split()) edges[frm - 1].append(to - 1) # -1 for 1-origin vertexes edges[to - 1].append(frm - 1) # if bidirectional K = int(input()) CS = list(int(x) - 1 for x in input().split()) INF = 9223372036854775807 dist = [] for c in CS: d = one_to_all_bfs(c, N, edges, INF) dd = [d[CS[i]] for i in range(K)] if INF in dd: print(-1) return dist.append(dd) ret = tsp_not_return(K, dist) print(ret + 1)