/*
#include <iostream>
#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,min1,a[5000001],st,dr,c[5000001],i,j;
long long s;

int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    st=1; dr=1;
    c[1]=1; s=0;
    for(i=2;i<=n;i++)
    {
        if(a[i]>=a[c[dr]])
        {
            dr=dr+1;
            c[dr]=i;
        }
        else
        {
            while(dr>=st && a[c[dr]]>a[i])
                dr=dr-1;
            c[++dr]=i;
        }
        if(i>=k)
           {
               s=s+a[c[st]];
               //cout<<a[c[st]]<<" ";
           }
        while(i-c[st]+1>=k)
            st=st+1;
    }
    g<<s;
    return 0;
}
*/

#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

deque <int> c;
int a[5000001];

int main()
{   int n,k,i;
    long long s=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    c.push_back(1);
    for(i=2;i<=n;i++)
    {
        if(a[i]>=a[c.back()])
        {
            c.push_back(i);
        }
        else
        {
            while(!c.empty() && a[c.back()]>a[i])
                c.pop_back();
            c.push_back(i);
        }

        if(i>=k)
           {
               s=s+a[c.front()];
               // cout<<a[c.front()]<<" ";
           }
        while(i-c.front()+1>=k)
            c.pop_front();

    }
    g<<s;
    return 0;
}