import sys
input = sys.stdin.readline

class StrongConnection:
  def __init__(self, N):
    self.N = N + 1
    self.edges = []
  def csr(self):
    start = [0] * (self.N + 1)
    elist = [0] * len(self.edges)
    for e in self.edges:
      start[e[0] + 1] += 1
    for i in range(1, self.N + 1):
      start[i] += start[i - 1]
    counter = start[:]
    for e in self.edges:
      elist[counter[e[0]]] = e[1]
      counter[e[0]] += 1
    self.start = start
    self.elist = elist
  def add_edge(self, v, w): self.edges.append((v, w))
  def scc_ids(self):
    self.csr()
    N = self.N
    now_ord = group_num = 0
    visited = []
    low = [0] * N
    order = [-1] * N
    ids = [0] * N
    parent = [-1] * N
    stack = []
    for i in range(N):
      if order[i] == -1:
        stack.append(~i)
        stack.append(i)
        while stack:
          v = stack.pop()
          if v >= 0:
            if order[v] == -1:
              low[v] = order[v] = now_ord
              now_ord += 1
              visited.append(v)
              for i in range(self.start[v], self.start[v + 1]):
                to = self.elist[i]
                if order[to] == -1:
                  stack.append(~to)
                  stack.append(to)
                  parent[to] = v
                else:
                  low[v] = min(low[v], order[to])
          else:
            v = ~v
            if low[v] == order[v]:
              while True:
                u = visited.pop()
                order[u] = N
                ids[u] = group_num
                if u == v:
                  break
              group_num += 1
            if parent[v] != -1:
              low[parent[v]] = min(low[parent[v]], low[v])
    for i, x in enumerate(ids):
      ids[i] = group_num - 1 - x
    return group_num, ids
  def groups(self):
    group_num, ids = self.scc_ids()
    groups = [[] for _ in range(group_num)]
    for i, x in enumerate(ids):
      groups[x].append(i)
    return groups
n,m=map(int,input().split())
scc = StrongConnection(n)

e=[[] for _ in range(n+1)]
for _ in range(m):
    a,b=map(int,input().split())
    scc.add_edge(a,b)
    e[b].append(a)
g = scc.groups()
g=g[::-1][1:]
n=len(g)
print(n-1)
for i in range(n-1):
    l=g[i];t=g[i+1]
    print(l[-1],t[0])