#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=1005;
int n,m,ans,res,x;
int neg[N],pos[N];
int f[N*N];
int nc[N],pc[N];
void solve(int v,int c,int w){
	for(int t=1;c;t<<=1){
		int x = min(c,t);
		c-=x;
		if(v>0){
			for(int i=n*n*2;i>=1;i--)
				f[i+v*x] = max(f[i]+w*x,f[i+v*x]);
		}
		else{
			for(int i=v*x;i<=n*n*2;i++)
				f[i+v*x] = max(f[i]+w*x,f[i+v*x]);
		}
	}
}
signed main(){
	scanf("%lld%lld",&n,&m);
	for(int i=n;i>=1;i--){
		scanf("%lld",&neg[i]);
		res -= neg[i]*i;
		ans += neg[i];
		nc[i] = neg[i];
	}
	int t;
	scanf("%lld",&t);
	ans += t;
	for(int i=1;i<=n;i++){
		scanf("%lld",&pos[i]);
		res += pos[i]*i;
		ans += pos[i];
		pc[i] = pos[i];
	}
	if(res==m){
		printf("%lld\n",ans);
		return 0;
	}
	if(res<m){
		int p=-1;
		for(int i=n;i>=1;i--){
			if(res+i*neg[i] >= m){p=i; break;}
			res += i*neg[i];
			ans -= neg[i];
			nc[i]=0;
		}
		if(p==-1) {puts("impossible"); return 0;}
		int l=0,r=neg[p];
		while(l<r){
			int mid = (l+r+1)>>1;
			if(res+p*mid>=m) r=mid-1;
			else l=mid;
		}
		ans -= l;
		res += l*p;
		nc[p] -= l;
	}
	else{
		int p=-1;
		for(int i=n;i>=1;i--){
			if(res-i*pos[i]<=ans){p=i; break;}
			res -= i*pos[i];
			ans -= pos[i];
			pc[i]=0;
		}
		if(p==-1) {puts("impossible"); return 0;}
		int l=0,r=pos[p];
		while(l<r){
			int mid = (l+r+1)>>1;
			if(res-p*mid<=ans) r=mid-1;
			else l=mid;
		}
		ans -= l;
		res -= l*p;
		pc[p] -= l;
	}
	memset(f,-0x3f,sizeof(f));
	f[n*n] = 0;
	for(int i=1;i<=n;i++){
		if(nc[i]) solve(i,nc[i],-1);
		if(neg[i]-nc[i]) solve(-i,neg[i]-nc[i],1);
		if(pc[i]) solve(-i,pc[i],-1);
		if(pos[i]-pc[i]) solve(i,pos[i]-pc[i],1);
	}
	if(f[n*n+(m-res)]<-n*3) puts("impossible");
	else printf("%d\n",ans+f[n*n+(m-res)]);
	return 0;
}