import java.util.*;

class Main {
	static int INF = 2 << 27;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int c = sc.nextInt();
		int n = sc.nextInt();
		int[] a = new int[n];
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		
		int[][] dp = new int[n][c+1];
		for(int i = 0; i < n; i++) {
			Arrays.fill(dp[i], INF);
			dp[i][0] = 0;
		}
		
		
		
		
		for(int i = 0; i < n; i++) {
			for(int j = 0; j <= c; j++) {
				if(i != 0) {
					dp[i][j] = Math.min(dp[i-1][j],dp[i][j]);
				}
				
				if(dp[i][j] == INF) {
					continue;
				}
				for(int k = 0; k <= c; k++) {
					if(j + a[i]*k > c) break;
					dp[i][j + a[i]*k] = Math.min((dp[i][j] + k),dp[i][j + a[i]*k]);
					
				}
			}
		}
		int min = INF;
		for(int i = 0; i < n; i++) {
			min = Math.min(dp[i][c], min);
		}
		if(min == INF) {
			min = -1;
		}
		System.out.println(min);
		
		
		
		
	}
}