#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = (x << 1) + (x << 3) + (ch ^ 48);
    ch = getchar();
  }
  return x * f;
}
inline void write(int x) {
  static int sta[35];
  int top = 0;
  do {
    sta[++top] = x % 10, x /= 10;
  } while (x);
  while (top) putchar(sta[top--] + '0');
  return;
}
int n, K, m, cnt = -1, ans;
int a[1000000], b[1000000], flg[1000000], f[1000000];
int dis[100][100], d[1000000];
queue<int> q;
inline void bfs(int x) {
  for (int i = 1; i <= n + 1; i++) d[i] = 0x3f3f3f3f;
  d[x] = 0;
  q.push(x);
  while (!q.empty()) {
    int p = q.front();
    q.pop();
    for (int i = 1; i <= m; i++) {
      int y = p + b[i];
      if (y <= n + 1 && d[y] == 0x3f3f3f3f) d[y] = d[p] + 1, q.push(y);
      y = p - b[i];
      if (y >= 1 && d[y] == 0x3f3f3f3f) d[y] = d[p] + 1, q.push(y);
    }
  }
  for (int i = 1; i <= n + 1; i++)
    if (flg[i] != -1) dis[flg[i]][flg[x]] = dis[flg[x]][flg[i]] = d[i];
}
int main() {
  n = read(), K = read(), m = read();
  for (int i = 1; i <= K; i++) a[read()] = 1;
  for (int i = 1; i <= m; i++) b[i] = read();
  for (int i = n + 1; i; i--) a[i] ^= a[i - 1];
  for (int i = 1; i <= n + 1; i++) flg[i] = (a[i]) ? ++cnt : -1;
  for (int i = 1; i <= n + 1; i++)
    if (a[i]) bfs(i);
  for (int i = 1; i < (1 << (cnt + 1)); i++) f[i] = 0x3f3f3f3f;
  for (int i = 0; i < (1 << (cnt + 1)); i++) {
    if (f[i] == 0x3f3f3f3f) continue;
    for (int j = 0; j <= cnt; j++) {
      if (i >> j & 1) continue;
      for (int k = j + 1; k <= cnt; k++) {
        if (i >> k & 1) continue;
        f[i + (1 << j) + (1 << k)] =
            min(f[i + (1 << j) + (1 << k)], f[i] + dis[j][k]);
      }
    }
  }
  int ans = f[(1 << (cnt + 1)) - 1];
  if (ans == 0x3f3f3f3f)
    printf("-1\n");
  else
    printf("%d\n", f[(1 << (cnt + 1)) - 1]);
  return 0;
}
