#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <stdlib.h>     /* srand, rand */
#include <time.h>       /* time */
#define mt make_tuple
#define ll long long
#define eb emplace_back
#define fi first
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
#define scanVec(vec , n) for(int i = 0; i < n ; i++){ cin>>vec[i];}
#define printVec(vec , n) for(int i = 0; i < n ; i++){ cout<<vec[i]<<" ";}
#define mod(a,b) ((a%b +b)%b)
#define bit(x,i) (x&(1<<i))  //select the bit of position i of x
#define lowbit(x) ((x)&((x)^((x)-1))) //get the lowest bit of x
#define hBit(msb,n) asm("bsrl %1,%0" : "=r"(msb) : "r"(n)) //get the highest bit of x, maybe the fastest
#define max(a,b) (a<b?b:a)
#define min(a,b) (a>b?b:a)
#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
#define IN(i,l,r) (l<i&&i<r)
#define LINR(i,l,r) (l<=i&&i<=r)
#define LIN(i,l,r) (l<=i&&i<r)
#define INR(i,l,r) (l<i&&i<=r)
#define lastEle(vec) vec[vec.size()-1]
#define SZ(x) ((int)((x).size()))
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define us unsigned short
#define INF 1001001001
#define PI 3.1415926535897932384626

using namespace std;
 using namespace __gnu_pbds;
 template <typename T>
 using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;

void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}

//----------------------------------------------------------------------------------------------------------------------


void swap(char &a, char & b){
    char temp = a;
    a = b;
    b = temp;
}

const ll MOD = 998244353;
const int MAXN = 1e5 + 5;

//char grid[MAXN][MAXN];

void add_self(ll &a, ll b){
    a+= b;
    while(a > MOD){
        a-=MOD;
    }
}


ll inf = 1LL*1e18;

void no(){
    cout <<"NO" << endl;
    exit(0);
}

void yes(){
    cout <<"YES" << endl;
    exit(0);
}





bool check( ll c, vector< ll > & arr,ll k){
    ll ans = arr[1]/c;
    ll rem = arr[1]%c;
    for(int i = 2;i < arr.size();i++){
        ll cnt = (arr[i] + rem)/c;
        ans += cnt;
        if(arr[i] + rem < c){
            rem = arr[i];
        }else{
            rem = (arr[i] + rem)%c;
        }
    }
    return ans >= k;
}


int main(){

    int t;
    cin >> t;
    while(t--){
        int n;
        cin >> n;
        ll k; cin >> k;
        vector< ll > arr (n + 1);
        ll sum = 0;
        for(int i = 1;i <= n;i++){
            cin >> arr[i];
            sum += arr[i];
        }
        ll left = 1; ll right = sum + 10;
        ll ans = 0;
        while(left <= right){
            ll c = left + (right - left)/2;
            if(check(c,arr,k)){
                ans = max(c,ans);
                left = c + 1;
            }else{
                right = c - 1;
            }
        }

        cout << ans*k << endl;
    }

    return 0;
}