#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
#define int long long
#define pb push_back
#define s second
#define f first
#define pf push_front
#define inf 1000000000000000000
#define bitebi __builtin_popcountll
#define FOR( i , n ) for( int i = 0 ; i < n ; i ++ )
#define YES cout <<"YES\n"
#define NO cout << "NO\n"
#define debug cout << "Here Fine" << endl ;
#define pr pair < int , int >
#define fbo find_by_order // returns iterator
#define ook order_of_key // returns strictly less numbers than key
using namespace std ;
//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,fma")
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
const double Pi=acos(-1.0);
const double EPS=1E-8;
const int mod = 1000000007 ;
const int mod1 = 998244353 ;
const int N = 3e5 + 10 ;
mt19937 R(time(0));
map < int , int > ma , ma1 ;
int a[ N ] , b[ N ] , n , m ;
int check( int mid ){
int lf = m * n ;
FOR( i , n ){
int nd = 0 , gn = mid ;
if( a[ i ] * m <= gn ){
nd += m ;
gn = gn - a[ i ] * m ;
}
else{
nd = nd + ( gn + a[ i ] - 1 ) / a[ i ] ;
gn = 0 ;
}
if( gn != 0 ){
nd = nd + ( gn + b[ i ] - 1 ) / b[ i ] ;
}
lf = lf - nd ;
}
if( lf >= 0 ) return 1 ;
return -1 ;
}
void solve(){
cin >> n >> m ;
FOR( i , n ) cin >> a[ i ] ;
FOR( i , n ){
cin >> b[ i ] ;
a[ i ] = max( a[ i ] , b[ i ] ) ;
}
int ans = 0 , l = 0 , r = inf ;
while( l < r ){
int mid = ( l + r ) / 2 ;
if( check( mid ) == 1 ){
ans = max( ans , mid ) ;
l = mid + 1 ;
}
else r = mid ;
}
if( check( l ) == 1 ) ans = max( ans , l ) ;
if( check( r ) == 1 ) ans = max( ans , r ) ;
cout << ans << "\n" ;
}
signed main() {
ios_base::sync_with_stdio(0),cin.tie(NULL),cout.tie(NULL);
int t = 1 ;// cin >> t ;
while( t -- ){
solve() ;
}
}
