#include<bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define int long long
#define vi vector<int>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define vpii vector<pair<int, int>>
#define vc vector<char>
#define vb vector<bool>
#define mii map<int,int>
#define f0r(i,n) for(int i=0;i<n;i++)
#define FOR(i,k,n) for(int i=k;i<n;i++)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define in(a) int a; cin>>a
#define in2(a,b) int a,b; cin>>a>>b
#define in3(a,b,c) int a,b,c; cin>>a>>b>>c
#define in4(a,b,c,d) int a,b,c,d; cin>>a>>b>>c>>d
#define vin(v,n); vi v(n); f0r(i,n){cin>>v[i];}
#define out(a) cout<<a<<'\n'
#define out2(a,b) cout<<a<<' '<<b<<'\n'
#define out3(a,b,c) cout<<a<<' '<<b<<' '<<c<<'\n'
#define out4(a,b,c,d) cout<<a<<' '<<b<<' '<<c<<' '<<d<<'\n'
#define pout(a) cout<<a.first<<' '<<a.second<<'\n'
#define vout(v) for(auto u : v){cout<<u<<' ';} cout<<'\n'
#define dout(a) cout<<a<<' '<<#a<<'\n'
#define dout2(a,b) cout<<a<<' '<<#a<<' '<<b<<' '<<#b<<'\n'
#define yn(x); if(x){cout<<"YES"<<'\n';}else{cout<<"NO"<<'\n';}
const int leg = 1e9 + 7;
const int mod = 998244353;
using namespace std;
signed main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
//ifstream cin(".in");
//ofstream cout(".out");
in(n);
vin(a,n);
vin(b,n);
reverse(all(a));
reverse(all(b));
vi v, w;
f0r(i,n){
f0r(j, a[i]){
w.pb(i);
}
f0r(j, b[i]){
v.pb(i);
}
}
int m = (int)v.size();
int M = (int)w.size();
int ans = -m;
// vout(w); vout(v);
/*
bool ok = 0;
f0r(i,m){
int k = i;
int j = M - 1;
int ca = 0;
while(k >= 0){
if(w[j] > v[k])ca++;
if(w[j] < v[k]){
ok = 1;
break;
ca--;
}
k--; j--;
}
if(ok)break;
// dout(ca);
k = i + 1;
while(k < m){
// if(w[j] > v[k])ca++;
if(w[j] < v[k])ca--;
k++; j--;
}
// dout2(i,ca);
// dout(ca);
ans = max(ans,ca);
}
*/
//last one to work
int lo = -1;
int hi = m-1;
while(lo < hi){
int i = lo + (hi - lo + 1) / 2;
// dout(i);
int k = i;
bool ok = 0;
int j = M - 1;
int ca = 0;
while(k >= 0){
if(w[j] > v[k])ca++;
if(w[j] < v[k]){
ok = 1;
break;
ca--;
}
k--; j--;
}
if(ok){
hi = i-1;
}
else{
// dout(ca);
k = i + 1;
while(k < m){
// if(w[j] > v[k])ca++;
if(w[j] < v[k])ca--;
k++; j--;
}
// dout2(i,ca);
// dout(ca);
ans = max(ans,ca);
lo = i;
}
}
if(lo != -1){
int i = lo;
// dout(i);
int k = i;
bool ok = 0;
int j = M - 1;
int ca = 0;
while(k >= 0){
if(w[j] > v[k])ca++;
if(w[j] < v[k]){
ok = 1;
break;
ca--;
}
k--; j--;
}
if(ok){
hi = i-1;
}
else{
// dout(ca);
k = i + 1;
while(k < m){
// if(w[j] > v[k])ca++;
if(w[j] < v[k])ca--;
k++; j--;
}
// dout2(i,ca);
// dout(ca);
ans = max(ans,ca);
lo = i;
}
}
out(ans);
}
