from sys import stdin

def main():
    N, M, F = (int(x) for x in input().split())
    hova = [[] for _ in range(N)]
    for _ in range(M):
        A, B = stdin.readline().split()
        A = int(A) - 1; B = int(B) - 1
        hova[A].append(B)
        hova[B].append(A)
    jart = [0] * N
    szint = [F - 1]
    er = []
    while szint:
        for cs in szint:
            jart[cs] = 2
        szint2 = []
        for cs in szint:
            for cs2 in hova[cs]:
                if jart[cs2] < 2:
                    er.append((cs + 1, cs2 + 1))
                if jart[cs2] == 0:
                    jart[cs2] = 1
                    szint2.append(cs2)
        szint = szint2
    print(len(er))
    for e in er:
        print(*e)


main()