#include<stdio.h>
#include<stdlib.h>

#define MIN(a,b) ((a)<(b)?(a):(b))

void run(void){
  int c,n;
  scanf("%d%d",&c,&n);
  const int inf=1000000;
  int *dp=(int *)calloc(c+1,sizeof(int));
  for(int i=1;i<=c;i++) dp[i]=inf;
  while(n--){
    int a;
    scanf("%d",&a);
    for(int i=a;i<=c;i++) dp[i]=MIN(dp[i],dp[i-a]+1);
  }
  printf("%d\n",dp[c]!=inf?dp[c]:-1);
}

int main(void){
  run();
  return 0;
}