#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
void chkmin(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
void chkmax(T1 &x, T2 y) {
  if (x < y) x = y;
}
namespace fastio {
char rbuf[1 << 23], *p1 = rbuf, *p2 = rbuf, wbuf[1 << 23], *p3 = wbuf;
inline char getc() {
  return p1 == p2 &&
                 (p2 = (p1 = rbuf) + fread(rbuf, 1, 1 << 23, stdin), p1 == p2)
             ? -1
             : *p1++;
}
inline void putc(char x) { (*p3++ = x); }
template <typename T>
void read(T &x) {
  x = 0;
  char c = getchar();
  T neg = 0;
  while (!isdigit(c)) neg |= !(c ^ '-'), c = getchar();
  while (isdigit(c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
  if (neg) x = (~x) + 1;
}
template <typename T>
void recursive_print(T x) {
  if (!x) return;
  recursive_print(x / 10);
  putc(x % 10 ^ 48);
}
template <typename T>
void print(T x) {
  if (!x) putc('0');
  if (x < 0) putc('-'), x = ~x + 1;
  recursive_print(x);
}
template <typename T>
void print(T x, char c) {
  if (!x) putc('0');
  if (x < 0) putc('-'), x = ~x + 1;
  recursive_print(x);
  putc(c);
}
void print_final() { fwrite(wbuf, 1, p3 - wbuf, stdout); }
}  // namespace fastio
const int MAXN = 1e4;
const int MAXM = 100;
const int MAXK = 20;
const int MAXP = 1 << 20;
const int INF = 0x3f3f3f3f;
int n, k, m, a[MAXN + 5], b[MAXN + 5], l[MAXM + 5], id[MAXN + 5], pos[MAXK + 5];
int dis[MAXN + 5], d[MAXK + 5][MAXK + 5], cnt;
void bfs(int s) {
  queue<int> q;
  memset(dis, -1, sizeof(dis));
  dis[s] = d[id[s]][id[s]] = 0;
  q.push(s);
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    if (id[x]) d[id[s]][id[x]] = dis[x];
    for (int i = 1; i <= m; i++) {
      if (x + l[i] <= n + 1) {
        if (!~dis[x + l[i]]) dis[x + l[i]] = dis[x] + 1, q.push(x + l[i]);
      }
      if (x - l[i] >= 1) {
        if (!~dis[x - l[i]]) dis[x - l[i]] = dis[x] + 1, q.push(x - l[i]);
      }
    }
  }
}
int dp[MAXP + 5];
int main() {
  scanf("%d%d%d", &n, &k, &m);
  for (int i = 1, x; i <= k; i++) scanf("%d", &x), a[x] = 1;
  for (int i = 1; i <= m; i++) scanf("%d", &l[i]);
  for (int i = 1; i <= n + 1; i++) b[i] = a[i] ^ a[i - 1];
  for (int i = 1; i <= n + 1; i++)
    if (b[i]) id[i] = ++cnt, pos[cnt] = i;
  memset(d, 63, sizeof(d));
  for (int i = 1; i <= n + 1; i++)
    if (id[i]) bfs(i);
  memset(dp, 63, sizeof(dp));
  dp[0] = 0;
  for (int i = 0; i < (1 << cnt); i++) {
    if (dp[i] >= INF) continue;
    for (int j = 1; j <= cnt; j++)
      for (int l = 1; l < j; l++)
        if ((~i >> j - 1 & 1) && (~i >> l - 1 & 1))
          chkmin(dp[i | (1 << j - 1) | (1 << l - 1)], dp[i] + d[j][l]);
  }
  printf("%d\n", (dp[(1 << cnt) - 1] >= INF) ? -1 : dp[(1 << cnt) - 1]);
  return 0;
}
