import sys

# sys.setrecursionlimit(1000005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
md = 10**9+7
# md = 998244353

class UnionFind:
    def __init__(self, n):
        self.table = [-1]*n
        self.mem = [[u] for u in range(n)]
        self.cnt = n

    def root(self, u):
        stack = []
        while self.table[u] >= 0:
            stack.append(u)
            u = self.table[u]
        for v in stack: self.table[v] = u
        return u

    def same(self, u, v):
        return self.root(u) == self.root(v)

    def merge(self, u, v):
        u = self.root(u)
        v = self.root(v)
        if u == v: return False
        su = -self.table[u]
        sv = -self.table[v]
        if su < sv: u, v = v, u
        self.table[u] = -su-sv
        self.table[v] = u
        self.mem[u] += self.mem[v]
        self.mem[v].clear()
        self.cnt -= 1
        return True

    def member(self, u):
        return self.mem[self.root(u)]

    # グループの要素数
    def size(self, u):
        return -self.table[self.root(u)]

n, m = LI()
to = [[] for _ in range(n)]
deg = [0]*n
uv = set()
uf = UnionFind(n)
for _ in range(m):
    u, v = LI1()
    to[u].append(v)
    deg[v] += 1
    uv.add(u)
    uv.add(v)
    uf.merge(u, v)

topo = []
st = []
for u in range(n):
    if deg[u] == 0: st.append(u)

while st:
    u = st.pop()
    topo.append(u)
    for v in to[u]:
        deg[v] -= 1
        if deg[v] == 0: st.append(v)

if len(topo) == n:
    rank = [0]*n
    for i, u in enumerate(topo): rank[u] = i
    ans = []
    for uu in uf.mem:
        if len(uu) == 1: continue
        uu.sort(key=lambda x: rank[x])
        for i in range(len(uu)-1):
            u = uu[i]
            v = uu[i+1]
            ans.append((u, v))
    print(len(ans))
    for u, v in ans: print(u+1, v+1)
else:
    uv = list(uv)
    print(len(uv))
    for i in range(len(uv)):
        print(uv[i-1]+1, uv[i]+1)