#include <iostream> #include <vector> #include <utility> #include <atcoder/dsu> using namespace std; using ll = long long; using ull = unsigned long long; #define rep(i,n) for(int i=0; i<(n); i++) int N,M; vector<vector<int>> E; vector<int> inIdx; vector<int> F; vector<pair<int,int>> ans; void solve(vector<int> V){ vector<int> I; for(int i : V) if(inIdx[i] == 0) if(F[i]) I.push_back(i); for(int i=0; i<I.size(); i++){ int p = I[i]; for(int e : E[p]) if(0 == --inIdx[e]) I.push_back(e); } bool cy = false; for(int i : V) if(inIdx[i] != 0) cy = true; if(cy){ I.clear(); for(int i : V) if(F[i]) I.push_back(i); I.push_back(I.front()); } for(int i=0; i+1<I.size(); i++) ans.push_back(make_pair(I[i],I[i+1])); } void testcase(){ cin >> N >> M; E.resize(N); inIdx.assign(N,0); F.assign(N,0); atcoder::dsu G(N); rep(i,M){ int u,v; cin >> u >> v; u--; v--; E[u].push_back(v); inIdx[v]++; F[u] = F[v] = 1; G.merge(u,v); } for(auto& g : G.groups()) solve(g); cout << ans.size() << "\n"; for(auto a : ans) cout << (a.first+1) << " " << (a.second+1) << "\n"; } int main(){ testcase(); return 0; } struct ios_do_not_sync{ ios_do_not_sync(){ ios::sync_with_stdio(false); cin.tie(nullptr); } } ios_do_not_sync_inst;