#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,fata,spate,x,v[5000005],deq[5000005];
long long suma;
int main()
{   f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    fata=1;
    spate=0;
    for(int i=1;i<=n;i++)
    {   while(fata<=spate && v[i]<=v[deq[spate]])
            spate--;
        spate++;
        deq[spate]=i;
        if(deq[fata]<=i-k)
            fata++;
        if(i-k>=0)
            suma=suma+v[deq[fata]];
    }
    g<<suma;
    return 0;
}