Дфс

def dfs(start):     
    Visited[start] = True
    for t in V[start]:
        if Visited[t]==False:
            dfs(t)
n, m, s = map(int, input().split())
Visited = [False]*(n+1)
V = [set() for i in range(n+1)]
for i in range(m):
    u, v = map(int, input().split())
    V[u].add(v)
    V[v].add(u)

dfs(s)