from collections import defaultdict 
from collections import deque

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 topological(graph, deg):
    start = []
    for i in range(len(deg)):
        if deg[i] == 0:
            start.append(i)
    topo = []
    while start:
        v = start.pop()
        topo.append(v)
        for u in graph[v]:
            deg[u] -= 1
            if deg[u] == 0:
                start.append(u)
    return topo

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]

    G = [[] for _ in range(n)]
    deg = [0]*n
    uf = UnionFind(n)
    for u,v in Q:
        uz = dic[u]
        vz = dic[v]
        G[uz].append(vz)
        deg[vz] += 1
        uf.union(uz,vz)
    #print(G)
    unidic = defaultdict(list)
    for i in range(n):
        par = uf.find(i)
        unidic[par].append(i)
    

    #連結成分ごと
    ans = []
    for unit in unidic.values():
        start = deque([])
        for x in unit:
            if deg[x] == 0:
                start.append(x)
        topo = []
        while start:
            v = start.pop()
            topo.append(v)
            for u in G[v]:
                deg[u] -= 1
                if deg[u] == 0:
                    start.append(u)
        #print("U",unit)
        #print("Topo",topo)

        if len(topo) == len(unit): #トポロジカルソート可能
            for i in range(len(topo)-1):
                s = topo[i]; t = topo[i+1]
                sori = revdic[s]; tori = revdic[t]
                ans.append([sori,tori])
        else:
            if len(unit) == 1:
                continue
            else:
                for i in range(len(unit)):
                    s = unit[i-1]; t = unit[i] #i==0の時に最後を持ってくる
                    sori = revdic[s]; tori = revdic[t]
                    ans.append([sori,tori])

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


if __name__ == '__main__':
    main()