#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long int
const int MOD = 1000000007;
const int MOD2 = 998244353;
const int INF = LLONG_MAX / 2;
const int MAXN = 100000;
int primes[1000000];
/*void seive() {
fill(primes, primes + 1000000, 1);
primes[0] = primes[1] = 0;
for (int i = 2; i * i < 1000000; i++) {
if (primes[i]) {
for (int j = i * i; j < 1000000; j += i) {
primes[j] = 0;
}
}
}
}
bool isPrime(int n) {
if (n <= 1) return false;
for (int i = 2; i * i <= n; i++) {
if (n % i == 0) return false;
}
return true;
}
int gcd(int a, int b) {
if (a == 0) return b;
return gcd(b % a, a);
}*/
int power(int a, int b, int mod) {
int res = 1;
a %= mod;
while (b > 0) {
if (b & 1) res = res * a % mod;
a = a * a % mod;
b >>= 1;
}
return res;
}
// nCr % MOD for n < MOD
int nCrModP(int n, int r) {
if (r > n) return 0;
if (r == 0 || r == n) return 1;
int numerator = 1, denominator = 1;
for (int i = 0; i < r; i++) {
numerator = (numerator * (n - i)) % MOD;
denominator = (denominator * (i + 1)) % MOD;
}
return (numerator * power(denominator, MOD - 2, MOD)) % MOD;
}
// Lucas's Theorem
int lucas(int n, int r) {
if (r == 0) return 1;
return (lucas(n / MOD, r / MOD) * nCrModP(n % MOD, r % MOD)) % MOD;
}
bool isPossible(int capacity[] , int refilltime[] , int requiredCapacity, int time , int n){
int totalCapacity = 0;
for(int i = 0 ; i<n ; i++){
int d = ((time-1)/(refilltime[i]))+1;
totalCapacity += (d*capacity[i]);
}
return (totalCapacity>=requiredCapacity);
}
void solve() {
int requiredCapacity,n;
cin>>requiredCapacity>>n;
int capacity[n],refilltime[n];
for(int i = 0 ; i<n ; i++){
cin>>capacity[i];
}
for(int i = 0 ; i<n ; i++){
cin>>refilltime[i];
}
int l = 0 , r = 1e9;
int ans = -1;
while(l<=r){
int mid = (l+r)/2;
if(isPossible(capacity,refilltime,requiredCapacity,mid,n)){
ans = mid;
r = mid-1;
}
else{
l = mid+1;
}
}
cout<<ans<<endl;
}
signed main() {
ios::sync_with_stdio(false); cin.tie(NULL);
int t;
cin >> t;
while (t--) {
solve();
}
return 0;
}
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