4
1 2 3 4

3

#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
const int N=1e5+10;
long long a[N],b[N],ans=0;
int main(){
    ios_sync_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin>>n;
    for(int i=0;i<n;i++)    cin>>a[i];
    for(int i=0;i<(n+1)/2;i++){
        if(a[i]>a[n-i+1]){
            b[i]=a[n-i+1]-a[i];
        }else{
            b[n-i+1]=a[i]-a[n-i+1];
        }
    }
    for(int i=0;i<n;i++){
        long long m=min(b[i],b[i+1]);
        b[i]-=m;
        b[i+1]-=m;
        ans+=m;
        ans+=b[i];
    }
    cout<<ans<<endl;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
const int N=1e5+10;
long long a[N],b[N],ans=0;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)    cin>>a[i];
    for(int i=1;i<=(n+1)/2;i++){
        if(a[i]<a[n-i+1]){
            b[i]=a[n-i+1]-a[i];
        }else{
            b[n-i+1]=a[i]-a[n-i+1];
        }
    }
    for(int i=1;i<=n;i++){
        long long m=min(b[i],b[i+1]);
        b[i]-=m;
        b[i+1]-=m;
        ans+=m;
        ans+=b[i];
    }
    cout<<ans<<endl;
    return 0;
}