#include<bits/stdc++.h>
#define ll long long
#define gc getchar
#define maxn 100005
using namespace std;

inline ll read(){
	ll a=0;int f=0;char p=gc();
	while(!isdigit(p)){f|=p=='-';p=gc();}
	while(isdigit(p)){a=(a<<3)+(a<<1)+(p^48);p=gc();}
	return f?-a:a;
}int n;
ll m;
#undef ll
#define ll __int128

void write(ll x){
	if(x >= 10) write(x / 10) ;
	putchar('0' + x % 10) ;
}

ll a[maxn],d[maxn];

ll pre[maxn] , suf[maxn] ;
ll pre_cnt[maxn] , suf_cnt[maxn] ;

inline int solve(ll x){
	ll sum=n;
	for(int i=1;i<=n;++i){
		d[i]=(x + a[i] - 1) / a[i] * a[i] - a[i] , d[i] /= a[i] ;
		//if(i==n&&d[i]<d[i-1])sum=n-1;
	}
	for(int i=1;i<=n;i++){
		pre_cnt[i] = pre_cnt[i - 1] + max((ll)0 , d[i] - pre[i - 1]) * 2 ;
		pre[i] = max((ll)0 , d[i] - pre[i - 1]) ;
	}
	ll ans = n + pre_cnt[n] ;
	ll last = d[n] ;
	ll res = d[n] * 2 ;  
	for(int i = n - 1 ; i; i --){
		d[i] -= 1 ; 

		ans = min(ans , pre_cnt[i - 1] + res + max((ll)0 , d[i] - last - pre[i - 1]) * 2 + n + n - i) ;  
		res += max((ll)0 , d[i] - last) * 2 ;
		last = max((ll)0 , d[i] - last) ; 
	}
	return ans<=m;
}

int main(){
	int t=read();
	while(t--){
		n=read();m=read();
		ll l=0,r=1e12,ans=0;
		for(int i=1;i<=n;++i){
			a[i]=read(),d[i]=0;
			r=min(r,a[i]*m/2+1);
		}
		while(l<=r){
			ll mid=l+r>>1;
			if(solve(mid))ans=mid,l=mid+1;
			else r=mid-1;
		}
		//printf("%lld\n",ans);
		write(ans) ;
		putchar('\n') ; 
	}
	return 0;
}