//#pragma GCC optimize("Ofast,unroll-loops,O3")
//#pragma GCC target("avx,avx2,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,fma,tune=native")
#include<bits/stdc++.h>
//#include<bits/extc++.h>
//#pragma pack(1)
#define fast ios::sync_with_stdio(0); cin.tie(0);
#define int long long
#define pii pair<int,int>
#define x first
#define y second
#define N 300015
using namespace std;
//using namespace __gnu_pbds;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//typedef tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update> order_multiset;
//typedef tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> order_set;
int a[N],b[N],n,m;
bool check(unsigned long long val){
int cnt=0;
for (int i=1;i<=n;i++){
if (a[i]>b[i]){
if (a[i]*m<val){
cnt+=m;
unsigned long long newval=val-a[i]*m;
cnt+=(newval/b[i]+(newval%b[i]>0));
}
else cnt+=(val/a[i]+(val%a[i]>0));
}
else {
cnt+=(val/b[i]+(val%b[i]>0));
}
if (cnt>m*n) return 0;
}
return cnt<=m*n;
}
signed main(){
fast
cin>>n>>m;
for (int i=1;i<=n;i++) cin>>a[i];
for (int i=1;i<=n;i++) cin>>b[i];
unsigned long long l=0,r=5e18;
while (l<r){
int mid=(l+r)>>1;
if (check(mid)) l=mid+1;
else r=mid;
}
cout<<l-1<<'\n';
}
