#include <bits/stdc++.h>
#define REP(v, i, j) for (int v = i; v != j; v++)
#define FORI(v) for (auto i : v)
#define FORJ(v) for (auto j : v)
#define OUT(v, a) \
FORI(v) \
cout << i << a;
#define OUTS(v, a, b) \
cout << v.size() << a; \
OUT(v, b)
#define in(a, n) \
REP(i, 0, n) \
cin >> a[i];
#define SORT(v) sort(begin(v), end(v))
#define REV(v) reverse(begin(v), end(v))
#define MEMSET(m) memset(m, -1, sizeof m)
#define pb push_back
#define fi first
#define se second
#define detachIO \
ios_base::sync_with_stdio(false); \
cin.tie(0); \
cout.tie(0);
using namespace std;
template<typename _Tp, typename _Alloc = std::allocator<_Tp> >
bool operator==(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y) {
if(__x.size() != __y.size()) return false;
return std::equal(__x.begin(), __x.end(), __y.begin());
}
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<pii, pii> piiii;
const int MOD = 1e9+7;
struct modint {
long long val;
modint() = default;
modint(int _val): val(_val){}
modint operator+(modint b){ return ((this->val + b.val)%MOD); }
modint operator-(modint b){ return ((MOD + this->val - b.val)%MOD); }
modint operator*(modint b){ return ((this->val * b.val)%MOD); }
modint operator^(int a){
if(a==0)return 1;
if(a==1)return *this;
return (((*this)*(*this))^(a>>1))*((*this)^(a&1));
}
};
modint invert(modint a){
return a^(MOD-2);
}
modint operator/(modint a, modint b){
return a*invert(b);
}
vector<long long> a,b;
bool valid(long long n, long long m, long long t){
long long t0=t;
long long need=0;
REP(i,0,n){
t=t0;
if((need)>(n*m))break;
if(a[i]<=b[i]){
need+=(t+b[i]-1)/b[i];
if((need)>(n*m))break;
continue;
}
long long run=(t+a[i]-1)/a[i];
t-=min(run,m)*a[i];
need+=min(run,m);
if((need)>(n*m))break;
if(t>0)need+=(t+b[i]-1)/b[i];
if((need)>(n*m))break;
}
return (need)<=(n*m);
}
int main(){
detachIO;
long long n;cin>>n;
long long m;cin>>m;
REP(i,0,n){
long long x;cin>>x;a.pb(x);
}
REP(i,0,n){
long long x;cin>>x;b.pb(x);
}
long long l=0,r=2e16;
long long ans;
while(l<=r){
long long mid=(l+r)/2;
if(valid(n,m,mid))ans=mid,l=mid+1;
else r=mid-1;
}
cout<<ans<<'\n';
}
