#include <bits/stdc++.h> using namespace std; using ll = long long; const int N = 3e5+10; ll a[N], b[N]; int main(){ ios_base::sync_with_stdio(false); cin.tie(nullptr); ll n, m; 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 = 4e18, ans; while(l <= r){ ll mid = (l+r)>>1; ll needed = 0, extra = 0; for(int i = 1; i <= n; ++i){ if(mid <= max(a[i], b[i])*m){ extra += m-ceil(1.0*mid/max(a[i], b[i])); }else{ needed += ceil((1.0*mid-m*max(a[i], b[i]))/b[i]); } } if(extra >= needed) l = mid+1, ans = mid; else r = mid-1; } cout << r << '\n'; }