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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll n,m;
ll a[300005],b[300005];
bool check(ll key) {
  ll les1,les2,tmp;
  ll tot1 = 0,tot2 = 0;
  for(int i = 1;i <= n;i++) {
    if(a[i] > b[i]) {
      les1 = min(key / a[i] + (key % a[i] == 0 ? 0 : 1),(ll)m);
      tmp = key - a[i] * les1;
      if(tmp > 0) les2 = tmp / b[i] + (tmp % b[i] == 0 ? 0 : 1);
      else les2 = 0;
      tot1 += les1;
      tot2 += les2;
    } else {
      les2 = key / b[i] + (key % b[i] == 0 ? 0 : 1);
      tot2 += les2;
    }
    if(tot1 + tot2 > n * m) return false;
  }
  if(tot1 + tot2 <= n * m) return true;
  return false;
}
int main() {
  freopen("study.in","r",stdin);
  freopen("study.out","w",stdout);
  scanf("%lld%lld",&n,&m);
  for(int i = 1;i <= n;i++) scanf("%lld",a + i);
  for(int i = 1;i <= n;i++) scanf("%lld",b + i);
  ll l = 1,r = 1e18,mid;
  while(l < r) {
    mid = (l + r + 1) / 2;
    if(check(mid))
      l = mid;
    else r = mid - 1;
  }
  printf("%lld\n",l);
  return 0;
}