#include<fstream>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int N,K,deque[5000005],front,back,A[5000005];
long long sum;

int main()
{

front=1; back=0;

f>>N>>K;

for (int i=1;i<=N;i++)
{
    f>>A[i];

    while (back>=front&&A[deque[back]]>=A[i]) back--;
    deque[++back]=i;

    if (deque[front]==i-K) front++;

    if (i>=K) sum+=(long long)A[deque[front]];

}
g<<sum;
return 0;
}