# include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N = 200010;
int n;
int a[N];


int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for(int i = 1; i <= n; i ++) cin >> a[i];

    LL res = 0;
    for(int i = 1; i <= n; i ++)
    {
        if(i < n)
        {
            int t = min(a[i], a[i + 1]);
            res += t;
            a[i] -= t, a[i + 1] -= t;
        }
        if(i == n)
        {
            int t = min(a[i], a[1]);
            res += t;
            a[i] -= t, a[i + 1] -= t;
        }
    }
    cout << res << endl;
    system("pause");
    return 0;
}