#include <bits/stdc++.h>
#define NMAX 5000001

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

int n,k,v[NMAX],d[NMAX],back,front;

int main(){
    f>>n>>k;
    for(int i=1;i<=n;++i)
        f>>v[i];
    back=front=1;
    d[front]=1;
    long long Sum=0;
    for(int i=2;i<=n;++i){
        while(front<=back&&v[d[back]]>=v[i])
            back--;
        d[++back]=i;
        while(d[front]<i-k+1)
            front++;
        if(i>=k)
            Sum+=v[d[front]];
    }
    g<<Sum;
    return 0;
}