import std.algorithm, std.conv, std.range, std.stdio, std.string;

const inf = 10 ^^ 9;

void main()
{
  auto c = readln.chomp.to!int;
  auto n = readln.chomp.to!size_t;
  auto ai = readln.split.to!(int[]);

  ai = ai.sort().uniq.array;

  auto dp = new int[][](n+1, c+1);
  foreach (ref d; dp) d[] = inf;
  dp[0][0] = 0;

  foreach (i; 0..n)
    foreach_reverse (j; 0..c+1)
      if (dp[i][j] < inf)
        foreach (k; 0..c) {
          auto l = k * ai[i] + j;
          if (l > c) break;
          dp[i+1][l] = min(dp[i+1][l], dp[i][j] + k);
        }

  auto r = dp[$-1][$-1];
  writeln(r == inf ? -1 : r);
}