#include<fstream.h>
int cotetz[100001],S[100001],i,n,s;
	ifstream f("oo.in");
	ofstream g("oo.out");
int main (){
	f>>n;
	for(i=1;i<=n;i++)
		f>>cotetz[i];
	
	for(i=1;i<=n;i++)
		S[i]=cotetz[i]+cotetz[i+1];
	
	for(i=1;i<=n;i++)
		if(S[i]>S[i+1]&&S[i]>S[i-1]){
			S[i+1]=-1;
			S[i-1]=-1;
			S[i+2]=-1;
			S[i-2]=-1;
		if(S[1]>S[2]&&S[1]>S[n])
			S[n-1]=-1;
			S[n]=-1;
			S[i+1]=-1;
			S[i+2]=-1;
		}
	for(i=1;i<=n;i++)
		if(S[i]>=0)
			s+=S[i];
	
	g<<s;

return 0;
}