import sys
sys.setrecursionlimit(10**7)
from collections import defaultdict 

class UnionFind(object):
    def __init__(self, n=1):
        self.par = [i for i in range(n)]
        self.rank = [0 for _ in range(n)]
        self.size = [1 for _ in range(n)]
    def find(self, x):
        """
        x が属するグループを探索して親を出す。
        """
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]
    def union(self, x, y):
        """
        x と y のグループを結合
        """
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.rank[x] < self.rank[y]:
                x, y = y, x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
            self.par[y] = x
            self.size[x] += self.size[y]
    def is_same(self, x, y):
        """
        x と y が同じグループか否か
        """
        return self.find(x) == self.find(y)
    def get_size(self, x):
        """
        x が属するグループの要素数
        """
        x = self.find(x)
        return self.size[x]


def SCC(N, G, RG):
    order = []
    used = [0]*N
    group = [None]*N
    def dfs(s):
        used[s] = 1
        for t in G[s]:
            if not used[t]:
                dfs(t)
        order.append(s)
    def rdfs(s, col):
        #print(s)
        group[s] = col
        used[s] = 1
        for t in RG[s]:
            if not used[t]:
                rdfs(t, col)
        TS.append(s)
      
    for i in range(N):
        if not used[i]:
            dfs(i)
    used = [0]*N
    label = 0
    TSL = []
    for s in reversed(order):
        if not used[s]:
            TS = []
            rdfs(s, label)
            #TS.reverse()
            TSL.append(TS)
            label += 1
    return label, group, TSL


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)]
    RG = [[] for _ in range(n)]
    uf = UnionFind(n)
    for u,v in Q:
        uz = dic[u]
        vz = dic[v]
        G[uz].append(vz)
        RG[vz].append(uz)
        uf.union(uz,vz)

    #print(G)
    unidic = defaultdict(list)
    for i in range(n):
        par = uf.find(i)
        unidic[par].append(i)
    
    #print(unidic)
    

    #連結成分ごとにSCC
    ans = []
    #for L in unidic.values():
    LIST, Group, TT = SCC(n, G, RG)
    #print(LIST,Group,TT)
    prepar = -1
    for i,group in enumerate(TT):
        nowpar = uf.find(group[0])
        #print(i,prepar,nowpar)
        if i != 0 and prepar == nowpar: #一番初めではないし、今見てる塊が前とつながっている。
            pre = TT[i-1][0]
            oripre = revdic[pre]
            first = group[0]
            orifirst = revdic[first]
            ans.append([oripre, orifirst])
        else:
            prepar = nowpar
        
        if len(group) == 1: continue #一つだったらつなげる必要なし
        for j in range(len(group)):
            if j < len(group) - 1:
                s = group[j]; t = group[j+1]
            else:
                s = group[j]; t = group[0]
            oris = revdic[s]; orit = revdic[t]
            ans.append([oris, orit])

    print(len(ans))
    for ret in ans:
        print(*ret)


if __name__ == '__main__':
    main()