import sys
input = sys.stdin.readline


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


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


def non_rec_dfs(s):
    stack = []
    stack.append(s)
    par = [-1] * N
    while stack:
        u = stack.pop()
        seen[u] = 1
        if u >= 0:
            stack.append(~u)
            for v in G[u]:
                if v == par[u] or seen[v]:
                    continue
                par[v] = u
                stack.append(v)
        else:
            u = ~u
            if par[u] != -1:
                ans2.append((par[u] + 1, u + 1))

    return ans2

ans = topsort(G)
seen = [0] * N
if len(ans) == N:
    ans2 = []
    for a in ans:
        if seen[a]:
            continue
        non_rec_dfs(a)
    print(len(ans2))
    for a, b in ans2:
        print(a, b)

    

else:
    print(N)
    for i in range(N-1):
        print(i+1, i+2)
    print(N, 1)