import java.io.*; import java.util.*; import java.util.stream.*; public class Main { static int[] values; static int[][] dp; public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int c = sc.nextInt(); int n = sc.nextInt(); values = new int[n]; for (int i = 0; i < n; i++) { values[i] = sc.nextInt(); } dp = new int[n][c + 1]; for (int[] arr : dp) { Arrays.fill(arr, -1); } int ans = dfw(n - 1, c); if (ans >= Integer.MAX_VALUE / 2) { System.out.println(-1); } else { System.out.println(ans); } } static int dfw(int idx, int v) { if (v < 0) { return Integer.MAX_VALUE / 2; } if (v == 0) { return 0; } if (idx < 0) { return Integer.MAX_VALUE / 2; } if (dp[idx][v] < 0) { dp[idx][v] = Math.min(dfw(idx - 1, v), dfw(idx, v - values[idx]) + 1); } return dp[idx][v]; } } class Utilities { static String arrayToLineString(Object[] arr) { return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n")); } static String arrayToLineString(int[] arr) { return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new)); } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); StringBuilder sb = new StringBuilder(); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public int[] nextIntArray() throws Exception { return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }