#include<bits/stdc++.h>
using namespace std;
long long a,b,c,d,e,i,j,ii,jj,zx,xc,lef,rig,mid,A[300009],B[300009],f[300009],M;
int main(){
ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0);
cin>>a>>M;
for(i=1; i<=a; i++) cin>>A[i];
for(i=1; i<=a; i++) cin>>B[i];
for(i=1; i<=a; i++) A[i]=max(A[i],B[i]);
lef=0;rig=1000000000000000009LL;
while(1){
if(lef+1>=rig) break;
mid=(lef+rig)/2;
for(i=1; i<=a; i++){
f[i]=mid;
}
zx=0;
for(i=1; i<=a; i++){
if(f[i]>A[i]*M){
f[i]-=A[i]*M;
}else{
c=f[i]/A[i];
if(f[i]%A[i]!=0) c++;
zx+=M-c;
f[i]=max(0LL,f[i]-c*A[i]);
}
}
xc=0;
for(i=1; i<=a; i++){
if(f[i]<=0) continue;
c=f[i]/B[i];
if(f[i]%B[i]!=0) c++;
xc+=c;
if(xc>zx) break;
}
if(zx>=xc){
lef=mid;
}else{
rig=mid;
}
}
cout<<lef;
return 0;
}
