#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>#include <vector>#include <queue>#include <stack>#include <map>#include <set>#include <cmath>using namespace std;int n,m;int a[100010];bool cmp(int x,int y){	return x>y;}int main(){	scanf("%d%d",&n,&m);	for(int i=1;i<=m;i++) scanf("%d",&a[i]);	sort(a+1,a+1+m,cmp);		int now = n;	if(n==0||n==1)	{		printf("0\n");		return 0;	}		for(int i=1;i<=m;i++)	{		if(a[i] <= 0) break;		if(a[i]<now) 		{			now = now - a[i];			a[i+1]--;		}		else 		{			now = 0;			printf("%d\n",i);			break;		}		}	if(now!=0)	{		printf("Impossible\n");	}	return 0;}