sick_duck

    #include <cstdio>
    #include <vector>
    #include <string>

    std::vector<std::vector<int>> graph;
    std::vector<short> used;
    std::string res;

    void dfs( int v )
    {
      used[v] = 1;
      for (auto to : graph[v])
      {
        switch (used[to])
        {
        case 0:
          dfs(to);
          break;
        case 1:
          printf("-1");
          exit(0);
          break;
        }
      }
      used[v] = 2;
      res += std::to_string(v + 1) + " ";
    }

    int main()
    {
      // read graph
      int n = 0, m = 0;
      scanf("%i%i", &n, &m);
      if (n < 1 || m < 0 || n > 1e5 || m > 1e5) { printf("-1"); return 0; }

      graph.resize(n);
      for (int k = 0, i = 0, j = 0; k < m; k++)
        scanf("%i%i", &i, &j), graph[i - 1].push_back(j - 1);

      // check graph
      used.resize(n);

      for (int i = 0; i < n; i++)
        if (!used[i])
          dfs(i);

      std::reverse(res.begin(), res.end());
      printf("%s", res.c_str());

      return 0;
    }