#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)(a.size())
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
ll gcd(ll a,ll b){if(!b)return a;else return gcd(b,a%b);}
int main()
{
ll n,m;
cin>>n>>m;
vector<ll>a(n),b(n);
for(int i=0;i<n;i++)cin>>a[i];
for(int i=0;i<n;i++)cin>>b[i];
ll l = 0,r = 1e16;
while(r>=l){
ll mid = (l+r)/2;
bool ok = 1;
ll f = 0;
vector<ll>cnt(n,0);
for(int i=0;i<n;i++){
if(a[i]<=b[i]){
f += m;
continue;
}
cnt[i] = (mid+a[i]-1)/a[i];
cnt[i] = min(cnt[i],m);
f += m-cnt[i];
}
for(int i=0;i<n;i++){
ll tmp = mid - cnt[i]*a[i];
if(tmp<=0)continue;
if((tmp+b[i]-1)/b[i] <= f){
f -= (tmp+b[i]-1)/b[i];
}else{
ok = 0;
break;
}
}
if(ok)l = mid+1;
else r = mid-1;
}
cout<<r<<'\n';
}
