#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <cstring>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <map>
#define PI acos(-1.0)
#define ms(a) memset(a,0,sizeof(a))
#define msp memset(mp,0,sizeof(mp))
#define msv memset(vis,0,sizeof(vis))
using namespace std;
//#define LOCAL
int cmp(int a,int b){return a>b;}
int main()
{
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
#endif // LOCAL
    ios::sync_with_stdio(false);
    int wall,n;
    vector<int> v;
    while(cin>>wall>>n)
    {
        v.clear();
        int sum=0;
        for(int i=0;i<n;i++)
        {
            int t;
            cin>>t;
            sum+=t;
            v.push_back(t);
        }
        if(sum<wall)printf("impossible\n");
        else
        {sort(v.begin(),v.end(),cmp);
        int ans=0,cnt=0;
        for(int i=0;i<(int)v.size();i++)
        {
            if(cnt>=wall)break;
            else cnt+=v[i],ans++;
        }
        printf("%d\n",ans);}
    }
    return 0;
}