// Author: Teoman Ata Korkmaz
#include <bits/stdc++.h>
#define int int64_t
using namespace std;
///////////////////////////////////////////////////////////
int n,ans;
vector<int> a,b;
signed main(void){
cin>>n;
a.resize(n);
b.resize(n);
for(auto& i:a)cin>>i;
for(auto& i:b)cin>>i;
int pa=0,pb=0;
while(pa<n && pb<n){
if(a[pa]==0){
pa++;
continue;
}
if(b[pb]==0 || pb<=pa){
pb++;
continue;
}
int t=min(a[pa],b[pb]);
ans+=t;
a[pa]-=t;
b[pb]-=t;
}
pa=0,pb=0;
while(pa<n && pb<n){
if(a[pa]==0){
pa++;
continue;
}
if(b[pb]==0 || pb<pa){
pb++;
continue;
}
assert(pa==pb);
int t=min(a[pa],b[pb]);
a[pa]-=t;
b[pb]-=t;
}
pa=0,pb=0;
while(pa<n && pb<n){
if(a[pa]==0){
pa++;
continue;
}
if(b[pb]==0){
pb++;
continue;
}
assert(pb<pa);
int t=min(a[pa],b[pb]);
ans-=t;
a[pa]-=t;
b[pb]-=t;
}
cout<<ans<<endl;
}
