#include <bits/stdc++.h>
#define int long long
#define debug cout << "ok\n";
#define SQR(x) (1LL * ((x) * (x)))
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define pli pair<ll,int>
#define vi vector<int>
#define FAST ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef unsigned int ui;
using namespace std;
const int M = 1e9 + 7;
const int INF = 1e9 + 7;
const ll INFLL = (ll)2e18 + 7LL;
const ld PI = acos(-1);
const int dx[] = {1, -1, 0, 0, -1, 1, 1, -1};
const int dy[] = {0, 0, 1, -1, -1, -1, 1, 1};
template<class _, class __>
bool minimize(_ &x, const __ y){
if(x > y){
x = y;
return true;
} else return false;
}
template<class _, class __>
bool maximize(_ &x, const __ y){
if(x < y){
x = y;
return true;
} else return false;
}
template<class _,class __>
void Add(_ &x, const __ y) {
x += y;
if (x >= M) {
x -= M;
}
return;
}
template<class _,class __>
void Diff(_ &x, const __ y) {
x -= y;
if (x < 0) {
x += M;
}
return;
}
//--------------------------------------------------------------
const int MaxN = 1e6+7;
int n,m,a[MaxN],b[MaxN],res = 0;
bool check(int ans) {
int tmp = 0;
for (int i=1;i<=n;i++) {
if (a[i] * m >= ans) {
tmp += m - ((ans-1)/a[i] + 1);
}
else tmp -= (ans - a[i] * m - 1) / b[i] + 1;
maximize(tmp,-INFLL);
minimize(tmp,INFLL);
}
return tmp >= 0;
}
void sol() {
cin >> n >> m;
for (int i=1;i<=n;i++) cin >> a[i];
for (int i=1;i<=n;i++) cin >> b[i];
for (int i=1;i<=n;i++) maximize(a[i],b[i]);
int l = 1,r = 1e18;
while (l <= r) {
int mid = (l+r) >>1 ;
if (check(mid)) {
res = mid;
l = mid + 1;
}
else r = mid - 1;
}
cout << res;
}
signed main() {
// freopen("test.inp","r",stdin);
// freopen("test.out","w",stdout);
FAST
int t=1;
// cin >> t;
while (t--) sol();
}
