#include <iostream>
#include <fstream>
#include <queue>
using namespace std;
deque <int> c;
int n;
queue <int> p;
void pop()
{
    if (p.front()==c.front())
         c.pop_front();
}
void push(int x)
{
    if (c.empty())
    {
        c.push_back(x);
        return;
    }
    while (!c.empty()&&x<=c.back())
        c.pop_back();
    c.push_back(x);
}
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out"); //pop_back
    int i,k,x;
    in>>n>>k;
    for (i=1;i<=k;i++)
    {
        in>>x;
        push(x);
        p.push(x);
    }
    long long s=0;
           s=s+c.front();
    for (i=i;i<=n;i++)
    {
        pop();
        p.pop();
        in>>x;
        push(x);
        p.push(x);
               s=s+c.front();
    }
           s=s+c.front();
    out<<s;
    out.close();
    in.close();
    return 0;
}