func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long MOD = 1e9 + 7;   const int iinf = 1 << 29;   const long long llinf = 1ll << 60;   const double PI = 3.14159265;   mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());   long long mrand(long long B) { return (unsigned long long)rng() % B; }   long long cross(pair<long long, long long> p1, pair<long long, long long> p2) {     return p1.first * p2.second - p2.first * p1.second;   }   bool online(pair<long long, long long> a, pair<long long, long long> b,               pair<long long, long long> c) {     pair<long long, long long> p1{b.first - a.first, b.second - a.second};     pair<long long, long long> p2{c.first - a.first, c.second - a.second};     return cross(p1, p2) == 0;   }   void z_func(vector<int> &z, vector<int> &s, int n) {     int L = 0, R = 0;     for (int i = 1; i < n; i++) {       if (i > R) {         L = R = i;         while (R < n && s[R - L] == s[R]) R++;         z[i] = R - L;         R--;       } else {         int k = i - L;         if (z[k] < R - i + 1)           z[i] = z[k];         else {           L = i;           while (R < n && s[R - L] == s[R]) R++;           z[i] = R - L;           R--;         }       }     }   }   const int MXN = 1e5 + 1;   int n, m;   bool roots[MXN];   vector<int> g[MXN];   int listt[MXN];   vector<int> ans;   void fail() {     cout <<  -1 n ;     exit(0);   }   int dfs(int node) {     int request = -1;     for (auto &v : g[node]) {       int req = dfs(v);       if (req != -1 && request != -1 && req != request) fail();       if (req != -1) request = req;     }     if (request != -1 && listt[node] != request) fail();     if (request == -1) {       if (listt[node] == node) {         ans.push_back(node);         return -1;       } else {         return listt[node];       }     } else {       if (node == listt[node]) {         ans.push_back(node);         return -1;       }       return listt[node];     }   }   void work() {     cin >> n >> m;     for (int i = 0; i < m; ++i) {       int u, v;       cin >> u >> v;       roots[v] = true;       g[u].push_back(v);     }     for (int i = 1; i <= n; ++i) cin >> listt[i];     for (int i = 1; i <= n; ++i)       if (!roots[i]) dfs(i);     cout << ((int)(ans).size()) <<   n ;     for (auto &e : ans) cout << e <<   n ;   }   int main() {     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);     work();     return 0;   }   