#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long i, n, j,k,v[5000000],minim,s;

int main()
{

    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    for(i=1;i<=n;i++)
    {

        minim=v[i];
        if(minim>v[i+1])
            minim=v[i+1];
        if(minim>v[i+2])
            minim=v[i+2];

        s+=minim;
    }

    fout<<s;
   return 0;

}