#include <bits/stdc++.h>
using namespace std;
queue<int> q;
int n, m, a[10009], c[10009], dis[21][10009], k, dp[1 << 21], now[10009],
    b[10009], d[10009], tot, num[10009], cnt;
bool vis[10009];
inline int rd() {
  int x = 0;
  char c = getchar();
  bool f = 0;
  while (!isdigit(c)) {
    if (c == '-') f = 1;
    c = getchar();
  }
  while (isdigit(c)) {
    x = (x << 1) + (x << 3) + (c ^ 48);
    c = getchar();
  }
  return f ? -x : x;
}
inline void spfa(int s, int id) {
  memset(dis[id], 0x3f, sizeof(dis[id]));
  q.push(s);
  dis[id][s] = 0;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    vis[u] = 0;
    for (int i = 1; i <= m; ++i) {
      int x = u - a[i], y = u + a[i];
      if (x >= 1) {
        if (dis[id][x] > dis[id][u] + 1) {
          dis[id][x] = dis[id][u] + 1;
          if (!vis[x]) {
            vis[x] = 1;
            q.push(x);
          }
        }
      }
      if (y <= n + 1) {
        if (dis[id][y] > dis[id][u] + 1) {
          dis[id][y] = dis[id][u] + 1;
          if (!vis[y]) {
            vis[y] = 1;
            q.push(y);
          }
        }
      }
    }
  }
}
int main() {
  n = rd();
  k = rd();
  m = rd();
  int x;
  for (int i = 1; i <= k; ++i) x = rd(), now[x] = 1;
  for (int i = 1; i <= m; ++i) a[i] = rd();
  for (int i = n + 1; i >= 1; --i) {
    c[i] = (now[i] - now[i - 1] + 2) % 2;
  }
  for (int i = 1; i <= n + 1; ++i)
    if (c[i]) {
      ++tot;
      num[tot] = i;
      spfa(i, tot);
    }
  for (int i = 1; i <= tot; ++i)
    for (int j = i + 1; j <= tot; ++j) {
      b[++cnt] = (1 << i - 1) | (1 << j - 1);
      d[cnt] = dis[i][num[j]];
    }
  q.push(0);
  memset(dp, 0x3f, sizeof(dp));
  dp[0] = 0;
  for (int i = 0; i < (1 << tot); ++i) {
    for (int j = 1; j <= cnt; ++j)
      if (!(i & b[j])) {
        dp[i | b[j]] = min(dp[i | b[j]], dp[i] + d[j]);
      }
  }
  if (dp[(1 << tot) - 1] > 1e9)
    puts("-1");
  else
    printf("%d", dp[(1 << tot) - 1]);
  return 0;
}
