"""
from collections import deque
seged = list(map(int, input().split()))
n = seged[0]
m = seged[1]
fo = seged[2]
elek = []
for i in range(n+1):
    elek.append([])
osszes = []
for u in range(m):
    a = list(map(int, input().split()))
    elek[a[0]].append(a[1])
    elek[a[1]].append(a[0])
    osszes.append([a[0], a[1]])
sor = deque([fo])
szintek = [-1]*(n+1)
szintek[fo] = 0
megoldas = []
count = 0
while len(sor)>0:
    aktualis = sor.popleft()
    for i in elek[aktualis]:
        if(szintek[i] == -1):
            sor.append(i)
            szintek[i] = (szintek[aktualis]+1)
        if (szintek[i] -1 )== szintek[aktualis]:
            megoldas.append([aktualis, i])
            count += 1
print(count)
for i in range(len(megoldas)):
    print(megoldas[i][0], megoldas[i][1])
"""
            
import sys
from collections import deque

def read_ints():
    line = sys.stdin.buffer.readline()
    while line and line.strip() == b'':
        line = sys.stdin.buffer.readline()
    return list(map(int, line.split())) if line else []

n, m, fo = read_ints()

adj = [[] for _ in range(n + 1)]
edges = []

read_edges = 0
while read_edges < m:
    a = read_ints()
    if not a:
        continue
    x, y = a[0], a[1]
    adj[x].append(y)
    adj[y].append(x)
    edges.append((x, y))
    read_edges += 1

dist = [-1] * (n + 1)
dist[fo] = 0
q = deque([fo])

while q:
    u = q.popleft()
    for v in adj[u]:
        if dist[v] == -1:
            dist[v] = dist[u] + 1
            q.append(v)
ans = []
for a, b in edges:
    if abs(dist[a] - dist[b]) == 1:
        ans.append((a, b))

out = sys.stdout.write
out(str(len(ans)) + "\n")
for a, b in ans:
    out(f"{a} {b}\n")