#include <iostream>
#include <queue>
using namespace std;
typedef pair<int, int> P;

struct Graph
{
    int n;
    std::vector<std::vector<int>> g;
    
    Graph(){}
    
    Graph(int n) : n(n){
        g.resize(n);
    }
    
    void add_edge(int from, int to){
        g[from].push_back(to);
    }
};

struct UnionFind
{
    std::vector<int> par, sz;
    
    UnionFind(int n){
        par.resize(n);
        sz.resize(n);
        for(int i = 0; i < n; i++){
            par[i] = i;
            sz[i] = 1;
        }
    }
    
    int find(int i){
        if(i == par[i]) return i;
        return par[i] = find(par[i]);
    }
    
    bool same(int i, int j){
        return find(i) == find(j);
    }
    
    void unite(int i, int j){
        i = find(i), j = find(j);
        if(i == j) return;
        if(sz[i] < sz[j]) std::swap(i, j);
        par[j] = i;
        sz[i] += sz[j];
    }
    
    int size(int i){
        return sz[find(i)];
    }
};

vector<int> y[200005];

int main()
{
    int n, m;
    cin >> n >> m;
    Graph g(n);
    UnionFind uf(n);
    int d[200005]{0};
    for(int i = 0; i < m; i++){
        int u, v;
        cin >> u >> v;
        u--; v--;
        g.add_edge(u, v);
        uf.unite(u, v);
        d[v]++;
    }
    for(int u = 0; u < n; u++){
        y[uf.find(u)].push_back(u);
    }
    vector<P> ans;
    for(int r = 0; r < n; r++){
        if(uf.find(r) != r) continue;
        int l = -1;
        vector<P> t;
        queue<int> que;
        for(int u : y[r]){
            if(!d[u]) que.push(u);
        }
        while(que.size()){
            int u = que.front();
            que.pop();
            if(l != -1) t.push_back(P(l, u));
            l = u;
            for(int v : g.g[u]){
                d[v]--;
                if(!d[v]) que.push(v);
            }
        }
        if(t.size() == y[r].size() - 1){
            for(P p : t) ans.push_back(p);
        }
        else{
            int k = y[r].size();
            for(int i = 0; i < k; i++){
                ans.push_back(P(y[r][i], y[r][(i + 1) % k]));
            }
        }
    }
    cout << ans.size() << endl;
    for(P p : ans) cout << p.first + 1 << " " << p.second + 1 << endl;
}