#include <iostream>
#include <iomanip>
#include <cassert>
#include <vector>
#include <numeric>
#include <string>
#include <bitset>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <random>
#include <ctime>
#include <chrono>
using namespace std;
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)((x).size())
typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
//typedef __int128_t int128;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const char en = '\n';
const int INF = 1e9 + 7;
const ll INFLL = 1e18;
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#ifdef __APPLE__
#include "debug.h"
//#define debug(...) 42
#else
#define debug(...) 42
#endif
void solve() {
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];
a[i] = max(a[i], b[i]);
}
ll l = 0, r = 2e18;
auto check = [&](ll md) -> bool {
ll days = 0;
for (int i = 0; i < n; ++i) {
if (m * a[i] >= md) {
days += (md + a[i] - 1) / a[i];
}
else {
ll musor = md - a[i] * m;
days += m;
days += (musor + b[i] - 1) / b[i];
}
if (days > 1LL * n * m) {
return false;
}
}
return days <= 1LL * n * m;
};
while (r - l > 1) {
ll md = l + (r - l) / 2;
if (check(md)) {
l = md;
} else {
r = md;
}
}
cout << l << en;
}
int main() {
#ifdef __APPLE__
freopen("input.txt", "r", stdin);
#else
ios_base::sync_with_stdio(0);
cin.tie(0);
#endif
solve();
return 0;
}
