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

ifstream fin ("deque.in");
ofstream fout("deque.out");

const int NMAX=5000005;

int N,K;
deque <int> dq;
int A[NMAX];


int main(){

    fin>>N>>K;
    for(int i=1;i<=N;++i){
        fin>>A[i];
    }
    long long S=0;
    for(int i=1;i<=N;++i){

        while( dq.size() and A[i]<=A[dq.back()] )
            dq.pop_back();
        dq.push_back(i);

        if(dq.front()==i-K) dq.pop_front();
        if(i>=K) S+=A[dq.front()];
    }
    fout<<S;
}