import sys
input = sys.stdin.readline


from heapq import *
from collections import *
def topsort(G, s):
    Q = []
    count = defaultdict(int)
 
    for u in s:
        for v in G[u]:
            count[v] += 1
 
    for u in s:
        if count[u] == 0:
            heappush(Q, u)
 
    anslst = []
    while Q:
        u = heappop(Q)
        anslst.append(u)
        for v in G[u]:
            count[v] -= 1
            if count[v] == 0:
                heappush(Q, v)
 
    return anslst


class UnionFind(object):
    def __init__(self, n=1):
        self.par = [i for i in range(n)]
        self.rank = [0 for _ in range(n)]
        self.size = [1 for _ in range(n)]

    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.rank[x] < self.rank[y]:
                x, y = y, x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
            self.par[y] = x
            self.size[x] += self.size[y]

    def is_same(self, x, y):
        return self.find(x) == self.find(y)

    def get_size(self, x):
        x = self.find(x)
        return self.size[x]


N, M = map(int, input().split())
G = [[] for i in range(N)]
U = UnionFind(N)
for i in range(M):
    u, v = map(int, input().split())
    u, v = u - 1, v - 1
    U.union(u, v)
    G[u].append(v)

S = [set() for _ in range(N)]
for i in range(N):
    S[U.find(i)].add(i)

seen = set()
ans = []
for i in range(N):
    ui = U.find(i)
    if ui in seen:
        continue
    seen.add(ui)
    L = topsort(G, S[ui])
    if U.get_size(i) == len(L):
        for j in range(len(L) - 1):
            ans.append((L[j] + 1, L[j + 1] + 1))
    else:
        L = list(S[ui])
        for j in range(len(L) - 1):
            ans.append((L[j] + 1, L[j + 1] + 1))
        ans.append((L[-1] + 1, L[0] + 1))
    
print(len(ans))
for a, b in ans:
    print(a, b)