#pragma comment(linker, "/STACK:1024000000,1024000000")#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<map>#include<set>#include<queue>#include<stack>#include<iostream>using namespace std;typedef long long LL;const double pi=acos(-1.0),eps=1e-6;void File(){    freopen("D:\\in.txt","r",stdin);    freopen("D:\\out.txt","w",stdout);}template <class T>inline void read(T &x){    char c = getchar(); x = 0;    while(!isdigit(c)) c = getchar();    while(isdigit(c)) { x = x * 10 + c - ‘0‘; c = getchar(); }}const int maxn=100010;int m,n,k,a[maxn],r[maxn];vector<int>g[maxn];bool flag[maxn],fail,f[maxn];vector<int>ans;void dfs(int x,int y){    if(a[x]==x) y=x;    else  { if(a[x]!=y) fail=1; }    for(int i=0;i<g[x].size();i++) dfs(g[x][i],y);    if(f[x]) ans.push_back(x);}int main(){    scanf("%d%d",&n,&m);    for(int i=1;i<=m;i++)    {        int u,v; scanf("%d%d",&u,&v);        g[u].push_back(v); r[v]++;    }    for(int i=1;i<=n;i++) { scanf("%d",&a[i]); f[a[i]]=1; }    for(int i=1;i<=n;i++) if(r[i]==0) dfs(i,i);    if(fail) printf("-1\n");    else    {        printf("%d\n",ans.size());        for(int i=0;i<ans.size();i++) printf("%d\n",ans[i]);    }    return 0;}