#include <bits/stdc++.h>
using namespace std;
#define int long long int
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n;
cin>>n;
vector<int>arr(n),brr(n);
for(int i=0;i<n;i++)
cin>>arr[i];
for(int i=0;i<n;i++)
cin>>brr[i];
vector<int>x(arr.begin(),arr.end());
vector<int>y(brr.begin(),brr.end());
vector<tuple<int,int,int>>stk;
int left=0;
int ans=0;
for(int i=0;i<n;i++)//try to put ppl in slots above their pay
{
while(!stk.empty()&&y[i]>0)
{
auto &[b,slot,prevleft]=stk.back();
int c=left-prevleft;
if(c>0)break;
int assign=min(y[i],slot);
ans+=assign;
y[i]-=assign;
x[b]-=assign;
slot-=assign;
if(slot==0)
stk.pop_back();
}
left+=y[i];
if(x[i]>0)
{
stk.push_back({i,x[i],left});
}
}
// }
for(int i=0;i<n;i++)
{
int a=min(x[i],y[i]);
x[i]-=a;
y[i]-=a;
}
for(int i=0;i<n;i++)
{
ans-=y[i];
}
cout<<ans<<endl;
return 0;
}
