#include <bits/stdc++.h>
using namespace std;
const int maxn = 10010;
const int inf = 0x3fffffff;
int dp[1 << 20], w[20][20], d[maxn], x[20], a[100];
inline int rightZeroBit(int mask) {
  for (int i = 0;; i++) {
    if ((mask & (1 << i)) == 0) return i;
  }
  return -1;
}
int main() {
  int n, k, l;
  while (scanf("%d%d%d", &n, &k, &l) == 3) {
    for (int i = 0; i < k; i++) scanf("%d", &x[i]);
    for (int i = 0; i < l; i++) scanf("%d", &a[i]);
    sort(a, a + l);
    l = unique(a, a + l) - a;
    set<int> iset;
    for (int i = 0; i < k; i++) {
      pair<set<int>::iterator, bool> p;
      p = iset.insert(x[i] - 1);
      if (!p.second) iset.erase(p.first);
      p = iset.insert(x[i]);
      if (!p.second) iset.erase(p.first);
    }
    k = copy(iset.begin(), iset.end(), x) - x;
    for (int i = 0; i < k; i++) {
      fill(d, d + n + 1, inf);
      d[x[i]] = 0;
      priority_queue<pair<int, int> > pq;
      pq.push(make_pair(0, x[i]));
      while (!pq.empty()) {
        int s = pq.top().second;
        int t = -pq.top().first;
        pq.pop();
        if (d[s] != t) continue;
        for (int j = 0; j < l; j++) {
          if (s - a[j] >= 0 && d[s - a[j]] > t + 1) {
            d[s - a[j]] = t + 1;
            pq.push(make_pair(-d[s - a[j]], s - a[j]));
          }
          if (s + a[j] <= n && d[s + a[j]] > t + 1) {
            d[s + a[j]] = t + 1;
            pq.push(make_pair(-d[s + a[j]], s + a[j]));
          }
        }
      }
      for (int j = 0; j < k; j++) w[i][j] = d[x[j]];
    }
    fill(dp, dp + (1 << k), inf);
    dp[0] = 0;
    for (int mask = 0; mask < (1 << k); mask++) {
      int u = rightZeroBit(mask);
      if (u >= k) continue;
      for (int v = 0; v < k; v++)
        if ((mask & (1 << v)) == 0) {
          int _mask = mask ^ (1 << u) ^ (1 << v);
          dp[_mask] = min(dp[_mask], dp[mask] + w[u][v]);
        }
    }
    printf("%d\n", dp[(1 << k) - 1] == inf ? -1 : dp[(1 << k) - 1]);
  }
  return 0;
}
