#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#include<random>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (int)(Y);++(X))
#define reps(X,S,Y) for (int (X) = (int)(S);(X) < (int)(Y);++(X))
#define rrep(X,Y) for (int (X) = (int)(Y)-1;(X) >=0;--(X))
#define rreps(X,S,Y) for (int (X) = (int)(Y)-1;(X) >= (int)(S);--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())
#define Endl endl
#define NL <<"\n"
#define cauto const auto

using namespace std;
using ll=long long;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
template<class T> using vv=vector<vector<T>>;
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
//#undef NUIP
#ifdef NUIP
#include "benri.h"
#else
#define out(args...)
#endif
void ouT(ll x,int d=3){auto re=to_string(x);if((int)re.size()>d) re=x>0?"oo":"-oo";cout<<string(d-re.size(),' ')<<re<<",";}
#ifdef __cpp_init_captures
template<typename T>vector<T> table(int n, T v){ return vector<T>(n, v);}
template <class... Args> auto table(int n, Args... args){auto val = table(args...); return vector<decltype(val)>(n, move(val));}
#endif
template<class A,class B> pair<A,B> operator+(const pair<A,B> &p,const pair<A,B> &q){ return {p.X+q.X,p.Y+q.Y};}
template<class A,class B,class C,class D> pair<A,B>& operator+=(pair<A,B> &p,const pair<C,D> &q){ p.X+=q.X; p.Y+=q.Y; return p;}
template<class A,class B> pair<A,B> operator-(const pair<A,B> &p,const pair<A,B> &q){ return {p.X-q.X,p.Y-q.Y};}
template<class A,class B,class C,class D> pair<A,B>& operator-=(pair<A,B> &p,const pair<C,D> &q){ p.X-=q.X; p.Y-=q.Y; return p;}
template<class A,class B> istream& operator>>(istream &is, pair<A,B> &p){ is>>p.X>>p.Y; return is;}
template<class T=ll> T read(){ T re; cin>>re; return re;}
template<class T=ll> T read(const T &dec){ T re; cin>>re; return re-dec;}
template<class T=ll> vector<T> readV(const int sz){ vector<T> re(sz); for(auto &x:re) x=read<T>(); return re;}
template<class T=ll> vector<T> readV(const int sz, const T &dec){ vector<T> re(sz); for(auto &x:re) x=read<T>(dec); return re;}
vv<int> readG(const int &n,const int &m){ vv<int> g(n); rep(_,m){ cauto a=read<int>(1),b=read<int>(1); g[a].pb(b); g[b].pb(a);} return g;}
vv<int> readG(const int &n){ return readG(n,n-1);}
vv<int> readD(const int &n,const int &m){ vv<int> g(n); rep(_,m){ cauto a=read<int>(1),b=read<int>(1); g[a].pb(b); } return g;}
vv<int> readD(const int &n){ return readD(n,n-1);}
template<class T> vv<pair<int,T>> readG(const int &n,const int &m){ vv<pair<int,T>> g(n); rep(_,m){ cauto a=read<int>(1),b=read<int>(1); cauto c=read<T>(); g[a].eb(b,c); g[b].eb(a,c);} return g;}
template<class T> vv<pair<int,T>> readG(const int &n){ return readG<T>(n,n-1);}
template<class T> vv<pair<int,T>> readD(const int &n,const int &m){ vv<pair<int,T>> g(n); rep(_,m){ cauto a=read<int>(1),b=read<int>(1); cauto c=read<T>(); g[a].eb(b,c); } return g;}
template<class T> vv<pair<int,T>> readD(const int &n){ return readD<T>(n,n-1);}
#ifdef __cpp_init_captures
template<typename T> vector<T> readT(int n, T v){ return readV(n,v);}
template <class... Args> auto readT(int n, Args... args){ vector re(1,readT(args...));rep(_,n-1) re.eb(readT(args...));	return re;}
template<typename T, size_t... Is> void addadd(T& t1, const T& t2, integer_sequence<size_t, Is...>){ cauto l = { (get<Is>(t1) += get<Is>(t2), 0)... }; (void)l;}
template <typename...T>tuple<T...>& operator += (tuple<T...>& lhs, const tuple<T...>& rhs){	addadd(lhs, rhs, index_sequence_for<T...>{});	return lhs;}
template <typename...T>tuple<T...> operator +(tuple<T...> lhs, const tuple<T...>& rhs){ return lhs += rhs;}
template<typename T, size_t... Is> void subsub(T& t1, const T& t2, integer_sequence<size_t, Is...>){ cauto l = { (get<Is>(t1) -= get<Is>(t2), 0)... }; (void)l;}
template <typename...T>tuple<T...>& operator -= (tuple<T...>& lhs, const tuple<T...>& rhs){	subsub(lhs, rhs, index_sequence_for<T...>{});	return lhs;}
template <typename...T>tuple<T...> operator - (tuple<T...> lhs, const tuple<T...>& rhs){ return lhs -= rhs;}
template<class Tuple, size_t... Is> void read_tuple_impl(istream &is, Tuple& t, index_sequence<Is...>){((is >> get<Is>(t)), ...);}
template<class... Args> auto& operator>>(istream &is, tuple<Args...>& t){ read_tuple_impl(is, t, index_sequence_for<Args...>{}); return is;}
#endif
#define TT cauto TTT=read();rep(_,TTT)
const ll MOD=1e9+7; //998244353;

struct UF{
  vector<int> data;
  UF(const int &size):data(size,-1){}
  int unite(int x, int y){
    x=root(x); y=root(y);
    if(x==y) return 0;
		if(-data[y]>-data[x]) swap(x,y);
		data[x]+=data[y]; data[y]=x;
    return y+1;
  }
  bool findSet(const int &x, const int &y){ return root(x)==root(y);}
  int root(const int &x){ return data[x]<0?x:data[x]=root(data[x]);}
  int size(const int &x){ return -data[root(x)];}
	int size(){ return count_if(all(data),[](const int &x){ return x<0;});}; //unverified
	int operator()(const int &x, const int &y){ return unite(x,y);}
	int operator()(const pii &xy){ return unite(xy.X,xy.Y);}
	int operator[](const int &x){ return root(x);}
	bool operator[](const pii &xy){ return findSet(xy.X,xy.Y);}
};

typedef vv<int> Graph;
struct Scc{
  stack<int> S;
  vector<int> inS,low,num;
  int time=0;
public:
  Graph dag;
  vector<int> inv;
  vv<int> scc;
  void visit(const Graph &g, int v){
    low[v] = num[v] = ++time;
    S.push(v); inS[v]=1;
    for(const int  &w:g[v]){
      if(!num[w]){
				visit(g,w);
				low[v]=min(low[v],low[w]);
      }else if(inS[w]) low[v]=min(low[v],num[w]);
    }
    if(low[v]==num[v]){
      scc.eb();
      while(1){
				int w = S.top(); S.pop(); inS[w]=0;
				scc.back().pb(w);
				if(v==w) break;
      }
    }
  }
  Scc(const Graph &g) {
    const int n = g.size();
    num.resize(n); low.resize(n); inS.resize(n);
    rep(u,n)if(!num[u]) visit(g,u);
    reverse(all(scc));
    
    inv.resize(n); dag.resize(scc.size());
    rep(i,scc.size())for(auto v:scc[i]) inv[v]=i;
    rep(i,scc.size())for(auto v:scc[i])for(auto e:g[v])
			if(inv[e]!=i)	dag[i].pb(inv[e]);
  }
};


int main(){
	ios_base::sync_with_stdio(false); cin.tie(0);
	cout<<fixed<<setprecision(0);
	cauto n=read();
	cauto m=read();
	cauto g=Scc(readD(n,m));
	cauto N=g.dag.size();
	UF uf(N);
	rep(v,N)for(cauto &u:g.dag[v]) uf(u,v);
	vector<int> cy(N);
	rep(v,N)if(g.scc[v].size()>1) cy[uf[v]]=1;
	vv<int> vs(N);
	rep(v,N) for(cauto &u:g.scc[v]) vs[uf[v]].eb(u);
	vector<pii> es;
	rep(v,N)if(uf[v]==v){
		reps(i,1,vs[v].size()) es.eb(vs[v][i-1],vs[v][i]);
		if(cy[v]) es.eb(vs[v].back(),vs[v][0]);
	}
	cout<<es.size() NL;
	for(cauto &[a,b]:es) cout<<a+1<<" "<<b+1 NL;
	return 0;
}