#include<bits/stdc++.h>
using namespace std;
vector<int>vec[400005],v1[400005];
int n,dep[400005],go[400005],m,in[400005],out[400005],tim,cnt[400005];
void dfs1(int now,int fa){
	in[now]=++tim;
	dep[now]=dep[fa]+1;
	for(auto to:vec[now])dfs1(to,now);
	out[now]=tim;
}
int rt[400005],ls[10000005],rs[10000005],lazy[10000005],mx1[10000005],mx2[10000005],ans,tot;
void upd(int p,int v){
	mx1[p]+=v;
	mx2[p]+=v;
	lazy[p]+=v;
}
void pushdown(int p,int l,int r){
	if(!lazy[p])return;
	int mid=l+r>>1;
	if(!ls[p])ls[p]=++tot,mx2[tot]=mid;
	if(!rs[p])rs[p]=++tot,mx2[tot]=r;
	upd(ls[p],lazy[p]);
	upd(rs[p],lazy[p]);
	lazy[p]=0;
}
void pushup(int p){
	mx1[p]=max(mx1[ls[p]],mx1[rs[p]]);
	mx2[p]=max(mx2[ls[p]],mx2[rs[p]]);
}
void add(int &p,int l,int r,int x,int y,int val){
	if(x>y)return;
	if(!p)p=++tot,mx2[p]=r;
	if(x<=l&&r<=y){
		upd(p,val);
		return;
	}
	pushdown(p,l,r);
	int mid=l+r>>1;
	if(x<=mid)add(ls[p],l,mid,x,y,val);
	if(y>mid)add(rs[p],mid+1,r,x,y,val);
	pushup(p);
}
int Getval(int p,int l,int r){
	if(!p||!mx1[p])return 0;
	if(l==r)return mx2[p];
	pushdown(p,l,r);
	int mid=l+r>>1;
	if(mx1[rs[p]])return max(mx2[ls[p]],Getval(rs[p],mid+1,r));
	return Getval(ls[p],l,mid);
}
int merge(int rt1,int rt2,int l,int r){
	if(!rt1||!rt2)return rt1|rt2;
	if(l==r){
		mx1[rt1]=mx1[rt1]+mx1[rt2];
		mx2[rt1]=mx2[rt1]+mx2[rt2]-l;
		return rt1;
	}
	if(!ls[rt1]&&!rs[rt1]){
		upd(rt2,lazy[rt1]);
		return rt2;
	}
	if(!ls[rt2]&&!rs[rt2]){
		upd(rt1,lazy[rt2]);
		return rt1;
	}
	pushdown(rt1,l,r),pushdown(rt2,l,r);
	int mid=l+r>>1;
	ls[rt1]=merge(ls[rt1],ls[rt2],l,mid);
	rs[rt1]=merge(rs[rt1],rs[rt2],mid+1,r);
	pushup(rt1);
	return rt1;
}
void dfs(int now,int fa){
	for(auto to:vec[now]){
		dfs(to,now);
		rt[now]=merge(rt[now],rt[to],1,n*2+1);
	}
	for(auto to:v1[now]){
		add(rt[now],1,n*2+1,1,dep[to],-1);
	}
	if(cnt[now]>0){
		add(rt[now],1,n*2+1,1,dep[now],cnt[now]);
	}
	ans=max(ans,Getval(rt[now],1,n*2+1)-dep[now]);
}
void Ins(int a,int b){
	if(a==b)return;
	if(in[b]<=in[a]&&in[a]<=out[b]);
	else puts("-1"),exit(0);
	cnt[a]++;
	v1[b].push_back(a);
}
int bel[200005],anc[200005],dfn[200005],low[200005],stk[200005],tp,ins[200005],cc,rnk[200005];
vector<int>scc[200005];
void tarjan(int now){
	dfn[now]=low[now]=++tim;
	stk[++tp]=now;
	ins[now]=1;
	for(auto to:vec[now]){
		if(!dfn[to])tarjan(to),low[now]=min(low[to],low[now]);
		else if(ins[to])low[now]=min(low[now],dfn[to]);
	}
	if(low[now]==dfn[now]){
		cc++;
		while(tp>0){
			int u=stk[tp--];
			scc[cc].push_back(u);
			bel[u]=cc;
			ins[u]=0;
			if(u==now)break;
		}
	}
}
void dfs2(int now,int fa,int rt){
	anc[now]=rt;
	for(auto to:vec[now]){
		if(to==fa||bel[to]==bel[now])continue;
		dfs2(to,now,rt);
	}
}
int frt[200005]; 
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d",&go[i]);
		if(i!=go[i])vec[go[i]].push_back(i);
	}
	for(int i=1;i<=n;i++){
		if(!dfn[i])tarjan(i);
	}
	for(int i=1;i<=cc;i++){
		if(scc[i].size()==1)continue;
		for(auto to:scc[i]){
			dfs2(to,0,to);
		}
	}
	for(int i=1;i<=n;i++){
		if(i==go[i])dfs2(i,0,i);
	}
	for(int i=1;i<=n;i++)vec[i].clear();
	for(int i=1;i<=cc;i++){
		if(scc[i].size()==1)continue;
		int tt=0,lst=0;
		reverse(scc[i].begin(),scc[i].end());
		for(auto to:scc[i]){
			rnk[to]=++tt;
			vec[lst].push_back(to);
			lst=to;
		}
		for(auto to:scc[i])frt[to]=scc[i][0];
		for(auto to:scc[i])vec[lst].push_back(to+n),lst=to+n;
	}
	for(int i=1;i<=n;i++){
		if(go[i]==i)vec[0].push_back(i);
		else{
			if(bel[go[i]]!=bel[i])vec[go[i]].push_back(i),vec[go[i]+n].push_back(i+n);
		}
	}
	scanf("%d",&m);
	tim=0;
	dfs1(0,0);
	for(int i=1;i<=m;i++){
		int a,b;scanf("%d%d",&a,&b);
		if(rnk[anc[a]]>=rnk[anc[b]])Ins(a,b),Ins(a+n,b+n);
		else Ins(a+n,b),Ins(a,frt[a]);
	}
	dfs(0,0);
	cout<<ans;
	return 0;
}