/*
IN THE NAME OF GOD
*/
#include <bits/stdc++.h>
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef long double ld;
#define F first
#define S second
#define Mp make_pair
#define pb push_back
#define pf push_front
#define size(x) ((ll)x.size())
#define all(x) (x).begin(),(x).end()
#define kill(x) cout << x << '\n', exit(0);
#define fuck(x) cout << "(" << #x << " , " << x << ")" << endl
#define endl '\n'
const int N = 3e5+23, lg = 18;
ll Mod = 1e9+7; //998244353;
inline ll MOD(ll a, ll mod=Mod) {a%=mod; (a<0)&&(a+=mod); return a;}
inline ll poww(ll a, ll b, ll mod=Mod) {
ll ans = 1;
a=MOD(a, mod);
while (b) {
if (b & 1) ans = MOD(ans*a, mod);
b >>= 1;
a = MOD(a*a, mod);
}
return ans;
}
ll n, m, a[N], b[N];
int main () {
ios_base::sync_with_stdio(false), cin.tie(0);
cin>>n>>m;
for(int i=1; i<=n; i++) cin>>a[i];
for(int i=1; i<=n; i++) cin>>b[i];
ll l=0, r=1e18;
while(r-l > 1) {
ll mid = (l+r)/2;
ll num = 0, yey = 1;
for(int i=1; i<=n; i++) {
if(a[i] >= b[i]) {
ll x = (mid+a[i]-1)/a[i];
x = min(x, m);
num -= (m-x);
ll f = mid - x*a[i];
num += max(0ll, (f-1+b[i])/b[i]);
} else {
ll x = (mid+a[i]-1)/b[i];
x = min(x, m);
num -= (m-x);
ll f = mid - x*b[i];
num += max(0ll, (f-1+b[i])/b[i]);
}
}
if(num <= 0) l=mid;
else r=mid;
}
cout<<l<<endl;
return 0;
}
