#include<cstdio>
#include<deque>

using namespace std;

typedef long long int lld;
typedef pair<int,int> PII;
const int NMAX = 5000000+5;

void Read(),Solve(),Print();

int N,K;
lld Sol;
int V[NMAX];
deque<PII> D;

int main()
{
    Read();
    Solve();
    Print();

    return 0;
}

void Read()
{
    int i;

    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    scanf("%d%d",&N,&K);

    for(i = 1; i <= N; i++)
        scanf("%d",&V[i]);
}

void Solve()
{
    int i;

    for(i = 1; i <= N; i++)
    {
        while(!D.empty() && D.front().first + K <= i) D.pop_front();
        while(!D.empty() && D.back().second >= V[i]) D.pop_back();
        D.push_back(make_pair(i,V[i]));
        if(i >= K) Sol += 1LL*D.front().second;
    }
}

void Print()
{
    printf("%lld\n",Sol);
}