#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define sp <<' '<<
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef vector<pii> vii;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
int n;
cin>>n;
vi x(n+1), y(n+1);
FORE(i,1,n+1) cin>>x[i];
FORE(i,1,n+1) cin>>y[i];
int ans=0;
vii vec;
FORE(i,1,n+1){
while(!vec.empty() and y[i]>0){
int ind=vec.back().se;
int deg=vec.back().fi;
vec.pop_back();
if(deg>y[i]){
y[i]=0;
deg-=y[i];
x[ind]-=y[i];
ans+=y[i];
vec.pb({deg,ind});
}
else{
ans+=deg;
x[ind]=0;
y[i]-=deg;
}
}
if(x[i]>0) vec.pb({x[i],i});
}
vec.clear();
FORE(i,1,n+1){
//cout<<"here" sp i sp x[i] sp y[i]<<endl;
y[i]-=x[i];
if(y[i]<0) y[i]=0;
ans-=y[i];
}
cout<<ans<<endl;
}
