#include <iostream>
#include <algorithm>
using namespace std;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

const int inf = 987654321;
int c, n;
vector<int> a;
vector<vector<int>> dp;

int nya(int i, int j) {
  if(dp[i][j] != -1) { return dp[i][j]; }
  if(i == n) { return dp[i][j] = c==j ? 0 : inf; }
  int res = inf, p = j;
  for(int x=0; p<=c; x++, p+=a[i]) {
    res = min(res, nya(i+1, p) + x);
  }
  return dp[i][j] = res;
}

int main(void) {
  scanf("%d%d", &c, &n);
  a.assign(n, 0);
  for(int i : range(n)) { scanf("%d", &a[i]); }
  dp.assign(n+10, vector<int>(c+10, -1));
  int res = nya(0, 0);
  if(res == inf) { res = -1; }
  printf("%d\n", res);
  return 0;
}