#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
#define p(x,y) pair<ll,ll>(x,y)
#define BIT(i,x) ((x>>i)&1)
#define MASK(x) (1<<x)
#define ld long double
#define __builtin_popcount __builtin_popcountll
#define pll pair<ll,ll>
template<class T1,class T2>
bool maximize(T1 &x,const T2 &y)
{
if(x<y)
{
x=y;
return 1;
}
return 0;
}
template<class T1,class T2>
bool minimize(T1 &x,const T2 &y)
{
if(x>y)
{
x=y;
return 1;
}
return 0;
}
void online()
{
std::ios_base::sync_with_stdio(0);
cin.tie(0);
#ifdef thuc
freopen("input.inp", "r", stdin);
freopen("output.out","w", stdout);
#else
#endif
}
const ll N=1e6+10;
ll n,m;
ll a[N],b[N],c[N];
ll check(ll x)
{
ll le=0;
for(int i=1;i<=n;i++)
{
c[i]=0;
if(a[i]>b[i])
{
ll z=min(m,(x+a[i]-1)/a[i]);
c[i]=a[i]*z;
le+=(m-z);
}
else le+=m;
}
for(int i=1;i<=n;i++)
{
if(c[i]<x)
le-=max(0ll,(x-c[i]+b[i]-1)/b[i]);
if(le<0) return 0;
}
return 1;
}
int main()
{
online();
cin>>n>>m;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
for(int j=1;j<=n;j++)
{
cin>>b[j];
}
ll base=0,d=1e18;
while(d)
{
while(check(base+d)) base+=d;
d/=2;
}
cout<<base;
}
