#include <bits/stdc++.h>
#include <fstream>
using namespace std;

int a[5000001];

int main(){
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k;
    fin>>n>>k;
    for(int i=0;i<n;i++) fin>>a[i];

    deque<int> dq;
    long long suma=0;
    for(int i=0;i<n;i++){
        while(!dq.empty() && a[dq.back()]>=a[i]) dq.pop_back();
        dq.push_back(i);
        while(!dq.empty() && dq.front()<=i-k) dq.pop_front();
        if(i>=k-1) suma+=a[dq.front()];
    }

    fout<<suma<<"\n";
    return 0;
}