#include<iostream>
#include<fstream>
#include<deque>
//#include<conio.h>
#include<algorithm>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define MN 5000001

int a[MN];
int64_t sum;
deque<int> D;

int main() {
    int n, k, i;
    fin>>n>>k;

    for(i=1; i<=n; ++i){
        fin>>a[i];

        while(!D.empty() && a[D.back()]>=a[i])
            D.pop_back();
        D.push_back(i);

        if(D.front()==i-k)
            D.pop_front();
        if(i>=k)
            sum+=a[D.front()];
    }

    fout<<sum;
    //getch();
    return 0;
}