#include<bits/stdc++.h>
using namespace std;
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define int long long
#define ordered_set tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>
#define fall(i,a,b) for(int i=a;i<=b;i++)
#define rfall(i,a,b) for(int i=a;i>=b;i--)
#define pb push_back
#define sz(x) (int)x.size()
const int MAXN=3e5+10;
typedef pair<int,int> pii;
int n,x[MAXN],y[MAXN],ans;
int32_t main(){
std::ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
fall(i,0,n-1) cin>>x[i];
fall(i,0,n-1) cin>>y[i],ans-=y[i];
stack<int> st;
fall(i,0,n-1){
while(sz(st) && y[i]){
auto j=st.top();
if(x[j]>y[i]){
x[j]-=y[i];
ans+=2*y[i];
y[i]=0;
break;
}
else{
y[i]-=x[j];
ans+=2*x[j];
x[j]=0;
st.pop();
}
}
if(x[i]) st.push(i);
}
fall(i,0,n-1){
int nd=min(x[i],y[i]);
ans+=nd;
}
cout<<ans<<"\n";
}
