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 + 1)
        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)

ans = topsort(G)
if len(ans) == N:
    print(N - 1)
    for i in range(N - 1):
        print(ans[i], ans[i + 1])
else:
    print(N)
    for i in range(N-1):
        print(i+1, i+2)
    print(N, 1)