import sys
sys.setrecursionlimit(10**7)

def main():
    N,M = map(int,input().split())
    Q = []
    S = set([])
    for i in range(M):
        U,V = map(int,input().split())
        Q.append((U,V))
        S.add(U)
        S.add(V)
    L = list(S)
    n = len(S) #出てくる頂点の種類
    L.sort()
    dic = {} #元の番号→座圧後の番号
    revdic = {} #座圧後の番号→元の番号
    for i in range(n):
        dic[L[i]] = i
        revdic[i] = L[i]
    ALL = [i for i in range(n)]
    ALL = set(ALL)
    G = [[] for _ in range(n)]
    for u,v in Q:
        uz = dic[u]
        vz = dic[v]
        G[uz].append(vz)
        ALL.discard(vz)
    
    used = set([])

    TS = []
    def dfs(v):
        if v in used:
            return
        used.add(v)
        for w in G[v]:
            if w in used:
                continue
            dfs(w)
            TS.append(w) #帰りがけで記録

    for root in ALL: #すべての始点について
      dfs(root)
      TS.append(root)
    TS.reverse() #最後に反転
    #print(TS)

    print(n-1) #何本か？
    for i in range(n-1):
        s = TS[i]
        t = TS[i+1]
        sori = revdic[s]
        tori = revdic[t]
        ret = [sori, tori]
        print(*ret)


if __name__ == '__main__':
    main()