#include <iostream>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <stdlib.h>
#include <time.h>
#include <map>
#include <complex>
#include <math.h>
#include <stack>
#include <unordered_map>
#include <set>
#include <string.h>
#include <iomanip>
#include <bitset>
#include <random>
using namespace std;
//#define int long long
#define P make_pair
#define A first
#define B second
typedef pair<int, int> pii;
struct H {
    int c, a;
    H() = default;
    H(int C, int A) :c(C), a(A) {}
};
H operator+(H x, H y) {
    return H(x.c + y.c, max(x.a + y.c, y.a));
}
int ls[30000010], rs[30000010], cnt;
H val[30000010];
void mdf(int i, int l, int r, int p, int x) {
    if (l == r) {
        int t = val[i].c + x;
        if (t == 0)val[i] = H(0, 0);
        else val[i] = H(t, l + t - 1);
        return;
    }
    int mid = (l + r) / 2;
    if (p <= mid) {
        if (ls[i] == 0)ls[i] = ++cnt;
        mdf(ls[i], l, mid, p, x);
    }
    else {
        if (rs[i] == 0)rs[i] = ++cnt;
        mdf(rs[i], mid + 1, r, p, x);
    }
    val[i] = val[ls[i]] + val[rs[i]];
}
int mg(int i, int j, int l, int r) {
    if (i == 0 || j == 0)return i + j;
    if (l == r) {
        int t = val[i].c + val[j].c;
        if (t == 0)val[i] = H(0, 0);
        else val[i] = H(t, l + t - 1);
        return i;
    }
    int mid = (l + r) / 2, k = ++cnt;
    ls[k] = mg(ls[i], ls[j], l, mid);
    rs[k] = mg(rs[i], rs[j], mid + 1, r);
    val[k] = val[ls[k]] + val[rs[k]];
    return k;
}
int fa[200010];
vector<int> sl[200010], rt;
int dfr[200010], ir[200010];
int tr[200010], nt[200010], rr[200010], rh[200010], dep[200010];
int kf[200010][25];
int dfs1(int u, int r) {
    if (u == r)dep[u] = 1;
    else dep[u] = dep[fa[u]] + 1;
    tr[u] = r;
    int ok = 0;
    for (int i = 0; i < sl[u].size(); i++) {
        if (sl[u][i] != r) { if (dfs1(sl[u][i], r))ok = 1, nt[u] = sl[u][i]; }
        else ok = 1, nt[u] = r;
    }
    if (ok)rr[u] = 1;
    return ok;
}
void dfs2(int u, int h, int r){
    rh[u] = h;
    for (int i = 0; i < sl[u].size(); i++) {
        if (sl[u][i] != r)dfs2(sl[u][i], (rr[sl[u][i]] ? sl[u][i] : h), r);
    }
}
int lca(int x, int y) {
    if (dep[x] > dep[y])swap(x, y);
    for (int k = 20; k >= 0; k--)if (dep[x] <= dep[kf[y][k]])y = kf[y][k];
    for (int k = 20; k >= 0; k--)if (kf[x][k] != kf[y][k])x = kf[x][k], y = kf[y][k];
    if (x == y)return x;
    return kf[x][0];
}
int ans = 0;
vector<int> al[200010], bl[200010], cl[200010];
int dfs3(int u) {
    int r = ++cnt;
    for (int i = 0; i < al[u].size(); i++)mdf(r, 1, 1000000, al[u][i], 1);
    for (int i = 0; i < sl[u].size(); i++)if (sl[u][i] != tr[u]) {
        int k = dfs3(sl[u][i]);
        r = mg(r, k, 1, 1000000);
    }
    for (int i = 0; i < bl[u].size(); i++)mdf(r, 1, 1000000, bl[u][i], -1);
    ans = max(ans, val[r].a - dep[u]);
    //cout << u << " " << val[r].a - dep[u] << endl;
    for (int i = 0; i < cl[u].size(); i++)mdf(r, 1, 1000000, cl[u][i], -1);
    return r;
}
signed main() {
    ios::sync_with_stdio(0);
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)cin >> fa[i], sl[fa[i]].push_back(i);
    for (int i = 1; i <= n; i++) {
        int k = i;
        while (1) {
            if (dfr[k] != 0 && dfr[k] != i)break;
            if (dfr[k] == i) {
                ir[k] = 1;
                rt.push_back(k);
                break;
            }
            dfr[k] = i;
            k = fa[k];
        }
    }
    for (int i = 0; i < rt.size(); i++)dfs1(rt[i], rt[i]);
    for (int i = 0; i < rt.size(); i++)dfs2(rt[i], rt[i], rt[i]);
    for (int i = 1; i <= n; i++)if (!ir[i])kf[i][0] = fa[i];
    for (int k = 1; k <= 20; k++)for (int i = 1; i <= n; i++)kf[i][k] = kf[kf[i][k - 1]][k - 1];
    int m, ok = 1;
    cin >> m;
    for (int I = 1; I <= m; I++) {
        int a, b;
        cin >> a >> b;
        int c = lca(a, b);
        if (c == 0)ok = 0;
        if (c == b) {
            al[a].push_back(dep[a]);
            bl[b].push_back(dep[a]);
            //cout << "A" << a << "B" << b << endl;
        }
        else if (rh[a] == rh[b]) ok = 0;
        else if (b != rh[b])ok = 0;
        else {
            al[a].push_back(dep[a]);
            cl[tr[a]].push_back(dep[a]);
            al[fa[tr[a]]].push_back(dep[a] + dep[fa[tr[a]]]);
            bl[b].push_back(dep[a] + dep[fa[tr[a]]]);
            //cout << "A" << a << "C" << tr[a] << endl << "A" << fa[tr[a]] << "B" << b << endl;
        }
    }
    if (ok == 0) {
        cout << -1 << endl;
        return 0;
    }
    for (int i = 0; i < rt.size(); i++)dfs3(rt[i]);
    cout << ans + 1 << endl;
    return 0;
}