#include<bits/stdc++.h>
#define ll long long
#define f first
#define s second
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define epb emplace_back
#define ull unsigned ll
using namespace std;
const ll linf = 3e18 + 1;
bool check(ll a[], ll b[], ll x, ll n, ll m){
ll cnt = 0;
for(int i = 1; i <= n; i++){
ll cnta;
if(b[i] >= a[i])cnta = 0;
else{
cnta = x / a[i];
if(x % a[i]) cnta++;
cnta = min(cnta, m);
}
ll cur = x - a[i] * cnta;
cnt += cnta;
if(cnt > n * m) return false;
if(cur < 0) continue;
else{
cnt += cur / b[i];
if(cur % b[i])cnt++;
if(cnt > n * m) return false;
}
}
return true;
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0);
ll n; cin >> n;
ll m; cin >> m;
ll a[n + 1];
ll b[n + 1];
for(int i = 1; i <= n; i++){
cin >> a[i];
}
for(int i = 1; i <= n; i++){
cin >> b[i];
assert (max (a[i],b[i]) <= 1e9);
}
ll l = 0, r = linf;
while(l + 1 < r){
ll mid = (l + r) / 2;
if(check(a, b, mid, n, m))l = mid;
else r = mid;
}
cout << l;
return 0;
}
