#define MAXN 5000001
#include <fstream>
using namespace std;
int K,N,A[MAXN],dq[MAXN];

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

long long deque(){int p,u,i;
p=1;u=0;
long long sum=0;

for (i=1;i<=N;i++)
    {
    while ((p<=u)&&(A[i]<=A[dq[u]])) u--;
    dq[++u]=i;
    if (dq[p]==i-K) p++;
    if (i>=K) sum+=A[dq[p]];
    }
return sum;
}

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


    return 0;
}