#include<bits/stdc++.h>
using namespace std;
#define ll long long
const bool Multitest = 0;
const int N = 3e5 + 10;
ll a[N], b[N]; int n, m;
bool check(ll val)
{
ll cnt = 0;
for(int i = 1 ; i <= n ; i++)
{
if(a[i] < b[i])
{
if(b[i] * n < val) return 0;
int l = 0, r = n, pos = -1;
while(l <= r)
{
int mid = (l + r) >> 1;
if(a[i] * mid + b[i] * (n - mid) >= val) l = mid + 1, pos = mid;
else r = mid - 1;
}
if(pos == -1) return 0;
cnt += pos;
}
}
for(int i = 1 ; i <= n ; i++)
{
if(a[i] < b[i]) continue;
if(a[i] * n > val)
{
int l = 1, r = n, pos = 0;
while(l <= r)
{
int mid = (l + r) >> 1;
if(a[i] * mid >= val) l = mid + 1, pos = mid;
else r = mid - 1;
}
cnt += pos;
}
else
{
int l = 1, r = n * m, pos = -1;
while(l <= r)
{
int mid = (l + r) >> 1;
if(a[i] * n + b[i] * mid >= pos) r = mid - 1, pos = mid;
else l = mid + 1;
}
if(pos == -1) return 0;
cnt -= pos;
}
}
return cnt >= 0;
}
void work()
{
cin >> n >> m;
for(int i = 1 ; i <= n ; i++) cin >> a[i];
for(int i = 1 ; i <= n ; i++) cin >> b[i];
ll l = 1, r = 1e18, pos = -1;
// cout << check(18) << '\n';
//
// return;
//
while(l <= r)
{
ll mid = (l + r) >> 1;
if(check(mid)) l = mid + 1, pos = mid;
else r = mid - 1;
}
cout << pos;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int q = 1;
if(Multitest) cin >> q;
while(q--) work();
}
