#include <iostream>
#include <fstream>
#include <vector>

#define maxn 5000010

using namespace std;

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

int n,k,li,ls;
long long s;
vector<int>v(maxn),a(maxn);

int main(){
    int i;
    f>>n>>k;
    for(i=1; i<=n; i++){
        f>>v[i];
    }

    li=1;ls=0;

    for(i=1; i<=n; i++){
        while(li<=ls && v[i]<=v[a[ls]])
        ls--;
        a[++ls]=i;
        if(a[li]==i-k)
            li++;
        if(i>=k)
            s+=v[a[li]];


    }

     g<<s;
    return 0;
}