#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
using ll=long long;
using ull=unsigned long long;
#define pi pair<int, int>
#ifdef LOCAL
#include"D:/Administrator/Documents/vscode/algo/debug.h"
#else
#define debug(...) 42
#endif
const int INF = 2e9 + 1000;
const ll INFLL = 8e18 + 1000;
mt19937 mrand(random_device{}());
void solve(){
    int n;
    cin>>n;
    vector<ll> a(n);
    for(auto &t:a)
    cin>>t;
    vector<ll> b(n);
    ll ans=0;
    for(int i=0;i<n;i++)
    {
        ll id=(i-1+n)%n;
        ll idx=(i+1)%n;
        ll t;
        if(a[id]-b[id]>a[idx]-b[idx])
        {
            t=min(a[i]-b[i],a[id]-b[id]);
            ans+=t;
            b[i]+=t;
            b[id]+=t;
        }else {
            t=min(a[i]-b[i],a[idx]-b[idx]);
            ans+=t;
            b[i]+=t;
            b[idx]+=t;
        }
    }
    cout<<ans;
}
signed main(){
#ifndef LOCAL
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
#endif
#ifdef LOCAL
    freopen("D:/Administrator/Documents/vscode/in.txt","r",stdin);
    freopen("D:/Administrator/Documents/vscode/out.txt","w",stdout);
#endif
    int T = 1;
   // cin >> T;
    while(T--) solve();
}