from collections import deque
class Unionfind:
     
    def __init__(self,n):
        self.uf = [-1]*n
 
    def find(self,x):
        if self.uf[x] < 0:
            return x
        else:
            self.uf[x] = self.find(self.uf[x])
            return self.uf[x]
 
    def same(self,x,y):
        return self.find(x) == self.find(y)
 
    def union(self,x,y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False
        if self.uf[x] > self.uf[y]:
            x,y = y,x
        self.uf[x] += self.uf[y]
        self.uf[y] = x
        return True
 
    def size(self,x):
        x = self.find(x)
        return -self.uf[x]

n,m = map(int,input().split())
uf = Unionfind(n+1)
e = [[] for i in range(n+1)]
deg = [0]*(n+1)
use = [0]*(n+1)
for _ in range(m):
    u,v = map(int,input().split())
    e[u].append(v)
    uf.union(u,v)
    use[u] = 1
    use[v] = 1
    deg[v] += 1
group = [[] for i in range(n+1)]
for i in range(n+1):
    if use[i]:
        group[uf.find(i)].append(i)
ans = []
for i in range(n+1):
    if group[i] == []:
        continue
    q = deque([])
    loop = 0
    for ind in group[i]:
        if deg[ind]:
            continue
        q.append(ind)
    order = []
    while q:
        now = q.pop()
        order.append(now)
        for nex in e[now]:
            deg[nex] -= 1
            if deg[nex] == 0:
                q.append(nex)
    if len(order) == len(group[i]):
        for x,y in zip(order,order[1:]):
            ans.append((x,y))
    else:
        for j in range(len(group[i])):
            x = group[i][j]
            y = group[i][(j+1)%len(group[i])]
            ans.append((x,y))
print(len(ans))
for x,y in ans:
    print(x,y)