#include<bits/stdc++.h>
using namespace std;
int n,m;
int p[200005],fa[200005],vist[200005];
int findfather(int x){
	return x==fa[x]?x:fa[x]=findfather(fa[x]);
}
vector<int>g[200005];
int bg[200005],en[200005],dep[200005],ff[200005],tot=0;
void dfs0(int x){
	bg[x]=en[x]=++tot;
	for(auto cu:g[x]){
		dep[cu]=dep[x]+1;ff[cu]=ff[x];
		dfs0(cu);
		en[x]=en[cu];
	}
}
int x[200005],y[200005];
vector<int>z1[200005],z2[200005];
struct apple{
	int s,t;//加的点数 最大可能值
	apple(int s=0,int t=0):s(s),t(t){}
	void operator+=(int x){
		s+=x;t=s?s:-1e9;
	}
}ss;
apple operator+(apple a,int b){
	return apple(a.s,a.t+b);
}
apple operator+(apple a,apple b){
	return apple(a.s+b.s,max(a.t,b.t));
}
apple sm[8000005];
int ls[8000005],rs[8000005],too=0;
void add(int x,int l,int r,int u,int v){
	if(l==r){
		sm[x]+=v;
		return;
	}
	int mid=(l+r)>>1;
	if(u<=mid){
		if(!ls[x])ls[x]=++too,sm[too]=ss;
		add(ls[x],l,mid,u,v);
	}else{
		if(!rs[x])rs[x]=++too,sm[too]=ss;
		add(rs[x],mid+1,r,u,v);
	}
	sm[x]=(sm[ls[x]]+sm[rs[x]].s)+(sm[rs[x]]+(mid-l+1));
}
int merg(int x,int y,int l,int r){
	if(!x||!y)return x+y;
	if(l==r){
		sm[x]+=sm[y].s;
		return x;
	}
	int mid=(l+r)>>1;
	int L=merg(ls[x],ls[y],l,mid);
	int R=merg(rs[x],rs[y],mid+1,r);
	ls[x]=L,rs[x]=R;
	sm[x]=(sm[ls[x]]+sm[rs[x]].s)+(sm[rs[x]]+(mid-l+1));
	return x;
}
int id[200005],ans=0;
void dfs1(int x){
	id[x]=++too;sm[too]=ss;
	for(auto cu:g[x]){
		dfs1(cu);
		id[x]=merg(id[x],id[cu],0,2*n);
	}
	for(auto cu:z1[x])add(id[x],0,2*n,cu,1);
	for(auto cu:z2[x])add(id[x],0,2*n,cu,-1);
	ans=max(ans,sm[id[x]].t-dep[x]);
}
int main(){
	ss.s=0;ss.t=-1e9;sm[0]=ss;
	scanf("%d",&n);
	for(int i=1;i<=n;++i)fa[i]=i;
	for(int i=1;i<=n;++i)scanf("%d",&p[i]);
	vector<int>v;
	for(int i=1;i<=n;++i){
		int fx=findfather(i),fy=findfather(p[i]);
		if(fx!=fy){
			fa[fx]=fy;g[p[i]].emplace_back(i);
			continue;
		}
		v.emplace_back(i);
	}
	for(auto z:v){
		ff[z]=z;dfs0(z);
		int zz=z;
		do{
			vist[zz]=1;zz=p[zz];
		}while(zz!=z);
	}
	scanf("%d",&m);
	for(int i=1;i<=m;++i){
		int a,b;
		scanf("%d%d",&a,&b);
		int fx=findfather(a),fy=findfather(b);
		if(fx!=fy){
			puts("-1");
			return 0;
		}
		if(!vist[b]){
			if(bg[b]>bg[a]||bg[a]>en[b]){
				puts("-1");
				return 0;
			}
		}
		x[i]=a,y[i]=b;
	}
	for(int i=1;i<=m;++i)if(x[i]!=y[i]){
		int a=x[i],b=y[i];
		if(bg[b]<=bg[a]&&bg[a]<=en[b]){
			z1[x[i]].emplace_back(dep[x[i]]);
			z2[y[i]].emplace_back(dep[x[i]]);
		}else{
			z1[a].emplace_back(dep[a]);
			//dep[a]+1
			//p[ff[a]] b
			z1[p[ff[a]]].emplace_back(dep[a]+1+dep[p[ff[a]]]);
			z2[b].emplace_back(dep[a]+1+dep[p[ff[a]]]);
		}
	}
	for(auto z:v)dfs1(z);
	printf("%d\n",ans);
	return 0;
}