#include <iostream>
#include <bits/stdc++.h>
#define NMAX 5000007
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int N,K,j,stop;
long long int rez;
int A[NMAX],v[NMAX];
int main()
{
    fin>>N>>K;
    for(int i=1;i<=N;i++)
        fin>>A[i];
    j=1;
    for(int i=1;i<K;i++)
    {
        while(j<=stop && A[i]<=A[v[stop]])
            stop--;
        v[++stop]=i;
    }
    for(int i=K;i<=N;i++)
    {
        if(v[j]==i-K)
            j++;
        while(j<=stop && A[i]<=A[v[stop]])
            stop--;
        v[++stop]=i;
        rez+=A[v[j]];
    }
    fout<<rez;
    return 0;
}