func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long INF = 1e13, Mo = 998244353;   const int N = 1000000;   const double eps = 1e-6;   namespace slow_IO {   long long read() {     long long x = 0;     int zf = 1;     char ch = getchar();     while (ch !=  -  && (ch <  0  || ch >  9 )) ch = getchar();     if (ch ==  - ) zf = -1, ch = getchar();     while (ch >=  0  && ch <=  9 ) x = x * 10 + ch -  0 , ch = getchar();     return x * zf;   }   void write(long long y) {     if (y < 0) putchar( - ), y = -y;     if (y > 9) write(y / 10);     putchar(y % 10 +  0 );   }   }  // namespace slow_IO   using namespace slow_IO;   vector<int> E1[N + 5], E2[N + 5];   int Flag1[N + 5], Flag2[N + 5];   int Ans[N + 5];   int ans = 0;   int main() {     int n = read(), m = read();     for (int i = (1); i <= (m); i++) {       int x = read(), y = read();       E1[x].push_back(y);       E2[y].push_back(x);     }     for (int i = (1); i <= (n); i++)       if (!Flag1[i]) {         Flag1[i] = Flag2[i] = 1;         for (int j = (0); j < (E1[i].size()); j++) Flag1[E1[i][j]] = 1;       }     for (int i = (n); i >= (1); i--)       if (Flag2[i]) {         for (int j = (0); j < (E2[i].size()); j++)           if (Flag2[E2[i][j]]) Flag2[i] = 0;       }     for (int i = (1); i <= (n); i++)       if (Flag2[i]) Ans[++ans] = i;     printf( %d n , ans);     for (int i = (1); i <= (ans); i++)       printf( %d%c , Ans[i], i == ans ?   n  :    );     return 0;   }   