#include<bits/stdc++.h>
#define ll __int128
#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;

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

__int128 a[maxn],d[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){
		sum += max((ll)0 , d[i] * 2) ;
		d[i + 1] -= max((ll)0 , d[i]) ; 
	}
	return sum<=m;
}

int main(){
	int t=read();
	while(t--){
		n=read();m=read();
		for(int i=1;i<=n;++i)
			a[i]=read(),d[i]=0;
		ll l=0,r=1e17,ans=0;
		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;
}