#include <fstream>
using namespace std;

int main()
{
   ifstream f("deque.in");
   ofstream g("deque.out");
   long long int n,subs,i,s;
   f>>n;
   f>>subs;

   int* a=new int[n+1];

   for(i=1;i<=n;i++)
    f>>a[i];
    s=0;
   for(i=1;i<=n-2;i++)
   {

       s=s+min(a[i],min(a[i+1],a[i+2]));

   }
g<<s;


}