#include<bits/stdc++.h> using namespace std; using i64 = long long; int main(){ ios_base::sync_with_stdio(false); cin.tie(NULL); int n; i64 m; cin >> n >> m; vector<i64> a(n); vector<i64> b(n); for(int i = 0;i < n;i++){ cin >> a[i]; } for(int i = 0;i < n;i++){ cin >> b[i]; a[i] = max(b[i],a[i]); } function<bool(i64)> f = [&](i64 x){ i64 have = 0; for(int i = 0;i < n;i++){ i64 tot = (x + a[i] - 1LL) / a[i]; if(tot <= m){ have += m - tot; } } for(int i = 0;i < n;i++){ i64 tot = (x + a[i] - 1LL) / a[i]; if(tot > m){ i64 tx = x - m * a[i]; assert(tx >= 0LL); tot = (tx + b[i] - 1LL) / b[i]; have -= tot; } } return have >= 0LL; }; i64 s = 0; i64 e = (i64)1e18 + 10LL; while(e > s){ i64 mid = (e + s + 1) / 2LL; if(f(mid)){ s = mid; }else{ e = mid - 1LL; } } cout << e << '\n'; return 0; }