#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MASK(i) (1LL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
#define block_of_code if(true)
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll gcd(ll a, ll b){return __gcd(a, b);}
ll lcm(ll a, ll b){return a / gcd(a, b) * b;}
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ll mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
double rngesus_d(double l, double r){
double cur = rngesus(0, MASK(60) - 1);
cur /= MASK(60) - 1;
return l + cur * (r - l);
}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b) {a = b; return true;}
return false;
}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b) {a = b; return true;}
return false;
}
template <class T>
void printArr(T container, string separator = " ", string finish = "\n", ostream &out = cout){
for(auto item: container) out << item << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
ll di(ll a, ll b){
return a / b + (a % b > 0);
}
int main(void){
ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);
clock_t start = clock();
int n; ll m; cin >> n >> m;
vector<ll> a(n), b(n);
for(int i = 0; i<n; ++i) cin >> a[i];
for(int i = 0; i<n; ++i) cin >> b[i];
ll l = 1, r = 1e18;
while(l < r){
ll mid = (l + r + 1) >> 1;
ll cnt = 0;
for(int i = 0; i<n; ++i){
ll cur = di(mid, max(a[i], b[i]));
if (cur <= m){
cnt += m - cur;
}
else{
ll fr = max(a[i], b[i]) * m;
fr = mid - fr;
cnt -= di(fr, b[i]);
}
}
if (cnt >= 0) l = mid;
else r = mid - 1;
}
ll mi = 1e18;
for(int i = 0; i<n; ++i) minimize(mi, max(a[i], b[i]));
if (l < mi) exit(1);
cout << l << "\n";
cerr << "Time elapsed: " << clock() - start << " ms\n";
return 0;
}
