#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define debug(v) \
cerr << "Line(" << __LINE__ << ") -> " << #v << " = " ;
#define dbx(x) debug(x); cerr << x << "\n";
#define dbg(x) debug(x); cerr << "{ "; for(auto &e : x) cerr << e << ", "; cerr << "} \n";
#define log(x) (31^__builtin_clz(x))
const int N = 1e6+10, MOD = 1e9+7;
void solve(){
int n, m; cin >> n >> m;
vector<int> a(n); for(int i = 0 ; i < n ; i ++)cin >> a[i];
vector<int> b(n); for(int i = 0 ; i < n ; i ++)cin >> b[i];
auto check = [&](ll mid){
ll _b = 0;
vector<ll> cur(n);
for(int i = 0 ; i < n ; i ++){
if(b[i] >= a[i]){
_b += m;
cur[i] = mid;
continue;
}
ll rt = mid / a[i] + (mid % a[i] > 0);
rt = min(rt, (ll)m);
_b += m - rt;
cur[i] = mid - (rt * a[i]);
cur[i] = max(cur[i], 0ll);
}
for(int i = 0 ; i < n ; i ++){
ll rt = cur[i] / b[i] + (cur[i] % b[i] > 0);
if(_b < rt){
return false;
}else {
_b -= rt;
}
}
return true;
};
ll l = 0, r = 2e18, ans = 0;
while (l <= r)
{
ll mid = (l + r) / 2;
if(check(mid)){
ans = mid;
l = mid + 1;
}else r = mid - 1;
}
cout << ans << "\n";
}
int main()
{
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cout.tie(nullptr);
// freopen("king2.in", "r", stdin);
// freopen("king2.out", "w", stdout);
int tc = 1; // cin >> tc;
for(int t = 1 ; t <= tc ; t ++){
solve();
}
return 0;
}
/*
*/
