#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("O3,unroll-loops") //main
//#pragma GCC target("avx2") //cf...
//#pragma GCC target("sse4") //Quera
#define B __int128
#define ll long long
typedef pair<int,int> pii;
typedef pair<int,pii> pip;
typedef pair<pii,int> ppi;
typedef pair<pii,pii> ppp;
#define f first
#define s second
#define lc 2*id
#define rc 2*id+1
#define all(x) x.begin(),x.end()
#define pb push_back
#define pp pop_back
#define unicorn(x) x.resize(unique(x.begin(),x.end())-x.begin())
string pr(int* vv,int l,int r){for(int i=l;i<r;i++)cout<<vv[i]<<" ";return "";}
string pr( ll* vv,int l,int r){for(int i=l;i<r;i++)cout<<vv[i]<<" ";return "";}
string pr(vector<int> vv){for(auto i:vv)cout<<i<<" ";return "";}
string pr( vector<ll> vv){for(auto i:vv)cout<<i<<" ";return "";}
string pr(pii* vv,int l,int r){for(int i=l;i<r;i++)cout<<"( "<<vv[i].f<<","<<vv[i].s<<" ) ";return "";}
string pr(vector<pii> vv){for(auto i:vv)cout<<"( "<<i.f<<","<<i.s<<" ) ";return "";}
random_device device;
default_random_engine rng(device());
#define randt(a,b) uniform_int_distribution<int64_t>(a,b)(rng)
const int L = 3e5+10,mod = 1e9+7;
const B inf = 1000ll*1000*1000*1000*1000*1000+10;
ll n,m;
ll a[L],b[L];
B cei(B x,B y){
return (x/y + (x%y != 0));
}
bool solve(B x){
B sum = 0;
for(int i=1;i<=n;i++){
if(a[i]*m >= x)
sum += ((B)a[i]*m-x)/a[i];
else
sum -= cei(x-a[i]*m,b[i]);
}
return (sum >= 0);
}
int main(){
//ofstream cout ("out.out");
//ifstream cin ("in.in");
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>a[i];
}
for(int i=1;i<=n;i++){
cin>>b[i];
}
for(int i=1;i<=n;i++){
a[i] = max(a[i],b[i]);
}
ll l=0,r=inf;
while(r-l > 1){
ll mid = (l+r)>>1;
if(solve(mid))
l = mid;
else
r = mid;
}
cout<<l<<endl;
}
