#include <fstream>
using namespace std;

int deq[5000010],n,i,s,a,k,p,u;

void push_back(int x){
  deq[u++];
}

void pop_back(){
  if (u>0)
    u--;
}
int pop_front(){
  return deq[p++];
}

int main(){
  ifstream f("deque.in",ifstream::in);
  f>>n;f>>k;
  f>>a;
  p=u=0;
  push_back(a);
  for (i=1;i<n;i++){
    if (i>2 && i<n-2)
      s+=pop_front();
	f>>a;
    while (deq[u-1]>a)
      pop_back();
    push_back(a);
  }
  ofstream g("deque.out",ifstream::out);
  g<<s;
  return 0;
}