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

int main()
{
	scanf("%d", &n);
	for(int i = 1; i <= n; i ++) scanf("%d", &a[i]);
	for(int i = 1; i <= n; i ++) temp[i] = a[i];
	
	LL res = 0;
	for(int i = 1; i <= n; i ++)
	{
		
		if(i < n) 
		{
			int t = min(temp[i], temp[i + 1]);
			res += t;
			temp[i] -= t, temp[i + 1] -= t;
		}
		else
		{
			int t = min(temp[n], temp[1]);
			res += t;
			temp[n] -= t, temp[1] -=t;
		}
	}
	for(int i = 1; i <= n; i ++) temp[i] = a[i];
	LL res1 = 0;
	for(int i = 1; i <= n; i ++)
	{
		if(i == 1)
		{
			int t = min(temp[n], temp[1]);
			res1 += t;
			temp[n] -= t, temp[1] -= t;
		}
		else
		{
			
			int t = min(temp[(n + i - 1) % n], temp[(n + i - 1) % n + 1]);
			res1 += t;
			temp[(n + i - 1) % n] -= t;
			temp[(n + i - 1) % n + 1] -= t;
		}
	}
	cout << max(res, res1) << endl;
	return 0;
		
	
}