#include <stdio.h>
#include <iostream>
#include <deque>

using namespace std;
FILE *f,*g;
int v[5000009];
deque <int> q;

int main()
{
    int n,k,i,j,x,y,ss=0;
    f=fopen("deque.in","r");
    g=fopen("deque.out","w");

    fscanf(f,"%d %d",&n,&k);
    for(i=1;i<=n;++i)
      fscanf(f,"%d",&v[i]);
    for(i=1;i<=n;++i)
    {
        while(!q.empty() && v[i]<=v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i>=k)
          ss+=v[q.front()];
        if(q.front()==i-k+1)
          q.pop_front();
    }
    fprintf(g,"%d",ss);

    fclose(f);
    fclose(g);
    return 0;
}