#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define db double
#define ll long long
#define pb push_back
#define fs first
#define sd second
#define Mod long(1e9 + 7)
#define all(x) x.begin(), x.end()
#define unvisited long(-1)
#define Eps double(1e-9)
#define _for(i, n) for(int i = 0; i < (n); i++)
#define dbg(x) cout << #x ": " << x << endl;
long long Max = 1e6 + 7, Inf = 2e18;
void print(bool x) { cout << (x ? "Yes" : "No") << endl; }
int ans = 0;
bool can(vector <int> &a, vector <int> &b, vector <int> &c, int x)
{ // cout << x << endl;
int win = 0LL, lose = 0LL, n = (int) c.size();
vector <int> r(n);
for(int i = 0; i < n; i++)
{
int v = abs(c[i] - x);
if(c[i] > x)
{
r[i] = c[i] - a[i] * (v / a[i]);
win = win + abs((int) v / a[i]);
}
if(c[i] < x)
{
r[i] = c[i] + b[i] * (v/b[i] + ((v%b[i]) != 0));
lose = lose + abs((int) v / b[i]) + abs((int) ((v%b[i]) != 0));
}
/*
if(win > lose) { win -= lose; lose = 0; }
if(lose > win) { lose -= win; win = 0; }*/
if(lose > Inf || win > Inf) return false;
if(c[i] == x) r[i] = c[i];
}
bool op = true;
if(win >= lose)
{
//cout << x << endl;
int temp = Inf;
for(int i = 0; i < n; i++)
{
// cout << r[i] << endl;
if(r[i] < x) op = false;
temp = min(temp, r[i]);
}
// cout << temp << endl;
ans = max(ans, temp);
return op;
}
else
return false;
return win >= lose;
}
/*
3 3
19 4 5
2 6 2
4 25
1 2 3 4
1 2 3 4
*/
void solve()
{
int n, m; cin >> n >> m;
vector <int> a(n), b(n), c(n);
for(auto& u : a) cin >> u;
for(auto& u : b) cin >> u;
int rx = Inf;
for(int i = 0; i < n; i++)
{
a[i] = max(a[i], b[i]);
c[i] = a[i] * m;
rx = min(rx, c[i]);
}
if(m == 1)
{
cout << rx << endl;
return;
}
int l = 0, r = Inf;
while(abs(l - r) != 1)
{
int middle = (l + r) / 2;
if(can(a, b, c, middle))
l = middle;
else
r = middle;
}
/*
for(int i = max(1LL, l - 10LL); i < l + 10LL; i++)
if(can(a, b, c, i)) l = i;*/
cout << ans << endl;
}
int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
// freopen("02-18.in", "r", stdin);
// freopen("output.txt", "w", stdout);
int Q = 1; //cin >> Q;
while(Q--)
{
solve();
}
return 0;
}
