#include <bits/stdc++.h>
using namespace std ;
const int MAX = 3e5 + 10 ;
int a[MAX] , b[MAX] ;
int n , m ;
bool check(long long x)
{
long long cnt = 0 ;
for(int i = 0 ; i < n ; ++i)
{
if(1ll * m * a[i] >= x)
cnt += m - (x + a[i] - 1ll) / a[i] ;
else
cnt -= (x - 1ll * m * a[i] + b[i] - 1ll) / b[i] ;
cnt = max(cnt , (long long)(-1ll * 1e18)) ;
}
return (cnt >= 0) ;
}
int main()
{
ios_base::sync_with_stdio(0) ;
cin.tie(0) ;
cin>>n>>m ;
for(int i = 0 ; i < n ; ++i)
cin>>a[i] ;
for(int i = 0 ; i < n ; ++i)
cin>>b[i] ;
for(int i = 0 ; i < n ; ++i)
a[i] = max(a[i] , b[i]) ;
long long l = 0 , r = 1e15 ;
long long ans = l ;
while(l <= r)
{
long long mid = (l + r) >> 1ll ;
if(check(mid))
ans = mid , l = mid+1ll ;
else
r = mid-1ll ;
}
return cout<<ans<<"\n" , 0 ;
}
