#include <bits/stdc++.h>
using namespace std;
int n, m, d[210000];
long long cnt[210000];
long long solve() {
  cnt[1] *= 2;
  cnt[n] *= 2;
  int Min = cnt[1], Max = cnt[1];
  for (int i = 1; i <= n; ++i) {
    if (Min > cnt[i])
      Min = cnt[i];
    else if (Max < cnt[i])
      Max = cnt[i];
  }
  if (Min == Max) {
    for (int i = 2; i <= n; ++i)
      if (d[i] - d[i - 1] != d[2] - d[1]) return -1;
    return cnt[1] * (d[n] - d[1]) - d[2] + d[1];
  } else {
    long long temp = 0;
    for (int i = 1; i < n; ++i) {
      temp += (d[i + 1] - d[i]) * min(cnt[i], cnt[i + 1]);
    }
    return temp;
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) scanf("%d", &d[i]);
  scanf("%d", &m);
  for (int i = 1; i <= m; ++i) {
    int temp;
    scanf("%d", &temp);
    ++cnt[temp];
  }
  printf("%I64d\n", solve());
  return 0;
}
