#include <bits/stdc++.h>

using namespace std;

#define ll long long
const int N=2e5+100;

ll n;
ll a[N];
ll ans;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>n;
    for(int i=0;i<n;i++)
        cin>>a[i];
    for(int i=0;i<n;i++)
    {
        if(a[(i-1+n)%n]>=a[i])
            ans+=a[i],a[(i-1+n)%n]-=a[i],a[i]=0;
        else
            ans+=a[(i-1+n)%n],a[i]-=a[(i-1+n)%n],a[(i-1+n)%n]=0;
    }
    cout<<ans<<endl;
    return 0;
}