#include <bits/stdc++.h>
using namespace std;
const int maxn = 10010;
const int inf = 0x3fffffff;
int d[maxn], x[20], a[100], dp[1 << 20], w[20][20];
bool vis[maxn];
int main() {
  int n, k, l;
  while (scanf("%d%d%d", &n, &k, &l) == 3) {
    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < k; i++) scanf("%d", &x[i]), vis[x[i]] = 1;
    for (int i = 0; i < l; i++) scanf("%d", &a[i]);
    sort(a, a + l);
    l = unique(a, a + l) - a;
    k = 0;
    for (int i = 0; i <= n; i++)
      if (vis[i] != vis[i + 1]) x[k++] = i;
    for (int i = 0; i < k; i++) {
      priority_queue<pair<int, int> > q;
      fill(d, d + n + 1, inf);
      d[x[i]] = 0;
      for (q.push(make_pair(0, x[i])); !q.empty();) {
        int u = q.top().second;
        int dis = -q.top().first;
        q.pop();
        if (d[u] != dis) continue;
        for (int j = 0; j < l; j++) {
          if (u - a[j] >= 0 && d[u - a[j]] > dis + 1)
            d[u - a[j]] = dis + 1, q.push(make_pair(-dis - 1, u - a[j]));
          if (u + a[j] <= n && d[u + a[j]] > dis + 1)
            d[u + a[j]] = dis + 1, q.push(make_pair(-dis - 1, u + 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;
      for (u = 0; u < k; u++)
        if ((mask & (1 << u)) == 0) break;
      if (u >= k) continue;
      for (int v = u + 1; 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;
}
