// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h>
using namespace std;
#define REP(i, s, e) for (int i = (s); i < (e); i++)
#define RREP(i, s, e) for (int i = (s); i >= (e); i--)
template <class T>
inline bool mnto(T& a, T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T& a, T b) {return a < b ? a = b, 1: 0;}
typedef long long ll;
typedef long double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int) _a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;
#ifndef DEBUG
#define cerr if (0) cerr
#endif
const int INF = 1000000005;
const ll LINF = 2000000000000000005ll;
const int MAXN = 300005;
int n, m;
int a[MAXN], b[MAXN];
ll need[MAXN];
bool isPos(ll x) {
ll ex = 0;
REP (i, 0, n) {
need[i] = x;
if (a[i] <= b[i]) {
ex += m;
continue;
}
ll use = min((ll) m, (x - 1) / a[i] + 1);
ex += m - use;
need[i] = max(0ll, x - use * a[i]);
}
REP (i, 0, n) {
if (need[i] == 0) {
continue;
}
ll use = (need[i] - 1) / b[i] + 1;
ex -= use;
if (ex < 0) {
return 0;
}
}
return ex >= 0;
}
int main() {
#ifndef DEBUG
ios::sync_with_stdio(0), cin.tie(0);
#endif
cin >> n >> m;
REP (i, 0, n) {
cin >> a[i];
}
REP (i, 0, n) {
cin >> b[i];
}
ll lo = 0, hi = LINF, mid;
while (lo < hi) {
mid = lo + hi + 1 >> 1;
if (isPos(mid)) {
lo = mid;
} else {
hi = mid - 1;
}
}
cout << lo << '\n';
return 0;
}
