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#include <bits/stdc++.h>
using namespace std;
int N, idx[100001];
bitset<100001> vis, ans;
vector<int> path;
unordered_set<int> G[100001];
void solve() {
vis.reset();
for (int i = 0; i < path.size() - 1; ++i) {
G[path[i]].erase(path[i + 1]);
}
memset(idx, -1, sizeof idx);
for (int i = 0; i < path.size(); ++i) idx[path[i]] = i;
int m = 0;
ans.set();
for (int i = 0; i < path.size() - 1; ++i) {
m = max(i + 1, m);
queue<int> q;
q.push(path[i]);
while (q.size()) {
int u = q.front();
q.pop();
if (vis[u]) continue;
vis[u] = 1;
if (u != path[i] && idx[u] != -1) {
for (int j = m; j < idx[u]; ++j)
ans[j] = 0;
m = max(idx[u], m);
continue;
}
for (auto& v : G[u]) {
if (!vis[v]) q.push(v);
}
}
}
vector<int> out;
for (int i = 1; i < path.size() - 1; ++i)
if (ans[i]) out.push_back(path[i]);
sort(begin(out), end(out));
cout << out.size() << '\n';
for (auto& x : out) cout << x << '\n';
}
void dfs(int u) {
vis[u] = 1;
path.push_back(u);
if (u == N) {
solve();
exit(0);
}
for (auto& v : G[u]) {
if (!vis[v]) dfs(v);
}
path.pop_back();
}
int main() {
int M; cin >> N >> M;
while (M--) {
int a, b; cin >> a >> b;
G[a].insert(b);
}
dfs(1);
}
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