#include<bits/stdc++.h>
#define maxn 105
#define mm(a,b) memset(a,b,sizeof(a))
using namespace std;
int a[maxn];
int main(){
//	freopen("input.txt","r",stdin);
	int n,k;
	cin>>n>>k;
	for(int i=1;i<=n;i++) cin>>a[i];
	int sum=0,left=0,day,flag=0;
	for(int i=1;i<=n;i++){
		left+=a[i];
		if(left>8){
			sum+=8;
			left-=8;
		}
		else{
			sum+=left;
			left=0;
		}
		if(sum>=k){
			day=i;
			flag=1;
			break;
		}
	}
	if(flag==0) cout<<"-1"<<endl;
	else cout<<day<<endl;
 	return 0;
}

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e2 + 17;
int n, k, have[5], cnt[5];
int main(){
	ios::sync_with_stdio(0), cin.tie(0);
	cin >> n >> k;
	have[2] = 2 * n, have[4] = n;
	for(int i = 0; i < k; i++){
		int x;
		cin >> x;
		while(x >= 3)
			if(have[4] > 0)
				x -= 4, have[4]--;
			else if(have[2] > 0)
				x -= 2, have[2]--;
			else
				return cout << "NO" << '\n', 0;
		if(x > 0)
			cnt[x]++;
	}
	while(cnt[2])
		if(have[2] > 0)
			cnt[2]--, have[2]--;
		else if(have[4] > 0)
			cnt[2]--, have[4]--, have[1]++;
		else
            cnt[2]--, cnt[1] += 2;
	if(cnt[1] > have[1] + have[2] + have[4] * 2)
		return cout << "NO" << '\n', 0;
	cout << "YES" << '\n';
	return 0;
}

#include<bits/stdc++.h>
#define maxn 100050
#define mm(a,b) memset(a,b,sizeof(a))
using namespace std;
vector<int>e[maxn];
int du[maxn]; 
double ans;
void dfs(int x,int fa,double epx,int deep){
	int len=e[x].size();
	for(int i=0;i<len;i++){
		int next=e[x][i];
		if(next==fa) continue;
		if(du[next]==1) ans+=epx*(deep+1);
		dfs(next,x,epx*1.0/(du[next]-1),deep+1);
	}
}
int main(){
//	freopen("input.txt","r",stdin);
	int n; cin>>n;
	for(int i=0;i<n;i++) e[i].clear();
	mm(du,0);
	for(int i=1;i<=n-1;i++){
		int u,v;
		cin>>u>>v;
		e[u].push_back(v);
		e[v].push_back(u);
		du[u]++,du[v]++;
	}
	dfs(1,0,1.0/du[1],0);
	printf("%.6lf\n",ans);
	return 0;
}