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

n, m = LI()
to = [[] for _ in range(n)]
deg = [0]*n
uv = set()
for _ in range(m):
    u, v = LI1()
    to[u].append(v)
    deg[v] += 1
    uv.add(u)
    uv.add(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:
    ans = []
    for i in range(n-1):
        u = topo[i]
        v = topo[i+1]
        if u in uv and v in uv:
            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)