#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#pragma GCC optimize("Ofast,unroll-loops,inline-functions,no-stack-protector,03")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,avx2,mmx,fma,avx,tune=native")
#pragma clang loop vectorize(enable)
#pragma clang loop interleave(enable)
#define int long long
#define sz(x) (int)x.size()
#define F first
#define S second
#define pb push_back
#define nl '\n'
#define o_set tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef pair<int, int> pii;
void file( string s = "" )
{
if( s.empty() )
return;
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
const int N = 3e5 + 2;
const int N1 = 1e6 + 2;
const int inf = 1e9;
const int INF = 1e18;
const int mod = 1e9 + 7;
const double eps = 1e-9;
int T = 1, n, m, a[N], b[N];
bool ch( int x )
{
int cnt = 0;
for( int i = 1; i <= n; ++i )
{
if( a[i] * m < x )
cnt += (x - a[i] * m + b[i] - 1) / b[i] + m;
else
cnt += (x + a[i] - 1) / a[i];
if( cnt > n * m )
return 0;
}
return 1;
}
void solve()
{
cin >>n >>m;
for( int i = 1; i <= n; ++i )
cin >>a[i];
for( int i = 1; i <= n; ++i )
cin >>b[i], a[i] = max(a[i], b[i]);
int l = 1, r = INF, mid, res = 1;
while( l <= r )
{
mid = (l + r) / 2;
if( ch(mid) )
l = mid + 1, res = mid;
else
r = mid - 1;
}
cout <<res;
}
signed main()
{
file("");
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
// cin >>T;
while( T-- )
solve();
}
